基于OFDMA细胞结构双层梁和继电器共享(IJCNIS-V3-N5-5)
https://www.sodocs.net/doc/0816212177.html,puter Network and Information Security , 2011, 5, 37-45
Published Online August 2011 in MECS (https://www.sodocs.net/doc/0816212177.html,/)
Bilayer Beams and Relay Sharing based OFDMA
Cellular Architecture
Yanxiong Pan 1,2
1
University of Science & Technology of China/Dept. of Electronic Engineering & Information Science, Hefei, China
2
Xichang Satellite Launch Center/Yibin Tracking Telemetry Station, Yibin, China
Email: yxpan8@https://www.sodocs.net/doc/0816212177.html,
Hui Han 3
, Sihai Zhang 1 and Wuyang Zhou 1
3
Chongqing Communication Institute of P.L.A/Dept. of Information Engineering, Chongqing, China
Email: haipiao@https://www.sodocs.net/doc/0816212177.html,; {shzhang, wyzhou}@https://www.sodocs.net/doc/0816212177.html,
Abstract —Over the past decade, researchers have been putting a lot of energy on co-channel interference suppres-sion in the forthcoming fourth generation (4G) wireless networks. Existing approaches to interference suppression are mainly based on signal processing, cooperative commu-nication or coordination techniques. Though good perfor-mance has been attained already, a more complex receiver is
needed, and there is still room for improvement through other ways.
Considering spatial frequency reuse, which provides an easier way to cope with the co-channel interference, this paper proposed a bilayer beams and relay sharing based (BBRS) OFDMA cellular architecture and corresponding frequency planning scheme. The main features of the novel architecture are as follows. Firstly, the base station (BS) uses
two beams, one composed of six wide beams providing cov-erage to mobile stations (MSs) that access to the BS, and the
other composed of six narrow beams communicating with fixed relay stations (FRSs). Secondly, in the corresponding frequency planning scheme, soft frequency reuse is consi-dered on all FRSs further. System-level simulation results demonstrate that better coverage performance is obtained and the mean data rate of MSs near the cell edge is improved significantly. The BBRS cellular architecture provides a practical method to interference suppression in 4G networks
since a better tradeoff between performance and complexity
is achieved.
Index Terms —interference, relay, OFDMA, cellular system,
frequency planning
I. I NTRODUCTION Orthogonal frequency division multiplexing (OFDM)
technique has high spectral efficiency and inherit
immunity to frequency selective fading, therefore the
corresponding multiplexing technique orthogonal frequency division multiple access (OFDMA) has already
become one of the key techniques of the candidates for the next generation (4G) mobile communication standards, such as 3GPP LTE-Advanced [1] and IEEE 802.16j [2]. In OFDM technique, the total system bandwidth is divided into several sub-carriers, and the spectra of two adjacent
sub-carriers have 50% overlap with each other, resulting in higher spectral efficiency compared with traditional frequency division multiplexing. When the bandwidth of each sub-carrier is smaller than the coherence bandwidth of the channel, the frequency selective fading channel can be converted into flat fading channel. Under the protection of the cyclic prefix, the inter symbol interference (ISI) resulted from multipath propagation is reduced significantly, thus better communication quality is achieved.
One of the basic features of 4G wireless network is broadband. According to the definition of the International
Telecommunication Union (ITU), 4G network must achieve a data rate higher than 100Mbps in the downlink, which urges to increase the utilization efficiency of the limited spectrum resource as much as possible. The extreme way called unitary frequency reuse, in which each cell uses the whole system bandwidth, can make better use of the spectrum resource, but may cause severe co-channel interference to cell edge users. If unitary frequency reuse cannot meet the system capacity requirement,
sectorization technique, in which the omnidirectional
antenna at the base station (BS) is replaced by several
sector antennas, is usually used. However, if aggressive
frequency reuse with each sector uses the whole system
bandwidth is adopted, and no effective interference
suppression measures are used, the interference will be even more unbearable. It is a very important way to enhance network performance by using special fixed relay stations (FRSs) to forward data to and thus boosting the performance of cell edge users [3]. However, the introduction of FRSs brings new challenges to frequency planning, thus more effort on interference suppression is needed.
A.Traditional Approaches to Interference Suppression Interference suppression in OFDMA networks has been a hot topic in recent years, with lots of effective methods being proposed, but most of them need a high complex receiver. Three ways to interference suppression are considered in 3GPP LTE system, i.e., interference randomization, interference cancellation and interference coordination/mitigation [1, 4]. Cell specific scramble codes, interleaving and frequency hopping techniques are used in interference randomization, but the interference power is only randomized over the whole system bandwidth and not actually decreased. Interference cancellation is based on interference detection and subtraction, and high complexity makes it usually been implemented at the base stations (BSs). However, in interference coordination/mitigation, restrictions on resource allocation between cells are considered. Though better Carrier to Interference plus Noise Ratio (CINR) is attained, it causes higher signaling overhead.
B.Frequency Planning Techinique
Careful frequency planning can suppress interference efficiently. A factor R I, which describes the ratio of interference from all BSs to that from all FRSs in downlink access zone (AZ), is introduced to model the interference status of each mobile station (MS) in [5]. According to different R I, the total system bandwidth is divided into three subsets, the first two of which can be used only by BS and FRS, respectively, and the other is used by BS and FRS simultaneously. It is a dynamic frequency planning scheme, in which better performance is achieved. But each BS sector uses the whole system bandwidth with no interference suppression strategies in downlink relay zone (RZ), leading to severe co-channel interference. Two adaptive frequency planning schemes are proposed in [6]. A better compromise between spectral efficiency and interference is achieved through frequency reuse factor (FRF) adaptation in different time zones. However, each BS sector can only use one third of the total system bandwidth in downlink AZ, resulting in lower system capacity.
C.Sectorization Techinique
The sectorization technique, in which each cell is covered by several sector antennas, is not only an approach to higher system capacity, but also a good method for interference suppression. Sector antenna only transmits radio signal to the directions concerned, thus the interference to other directions is reduced. However, in most previous works [5-6], relay stations are equipped with omnidirectional antennas, causing interference to stations transmitting on the same channel in all directions around. Furthermore, relay stations are usually placed in each BS sector, leading to higher costs when the network is larger.
A sector relay based cell architecture is proposed in [7]. Being able to communicate with the three nearest BSs simultaneously, FRSs equipped with three sector antennas are located on common vertices of hexagonal cells, thus the number of FRSs needed is dropped. But in each cell, the total system bandwidth is partitioned into seven parts, only one of which can be used by the BS and each FRS, respectively. Similarly, Lee et al proposed a shared relay segmentation (SRS) cell architecture [8]. Each BS and FRS has three sector antennas, using the whole and one third of the total system bandwidth, respectively. FRSs only located on those common vertices that BS antennas pointed to. Though cooperative communication between BS and FRS is adopted and no interference needs to be considered in the same BS sector, the interference between adjacent BS sectors in the same cell is still severe. An ideal sector antenna model, the border of which is a straight line, is used in [9], resulting in zero signal strength in some directions. In practice, a sector antenna radiates signal to all directions around it with different gains. Therefore, when the number of interfering stations is big, large errors will appear in the performance analysis.
In this paper, a bilayer beams and relay sharing based (BBRS) OFDMA cellular architecture and corresponding frequency planning scheme are proposed. Our contribution is threefold. Firstly, a novel architecture is designed. The two beam layers generated by sector antennas on each BS can be viewed as one type of space division multiplexing (SDM), which brings down the co-channel interference of aggressive frequency reuse and increases the mean data rate of cell edge users with that of cell central users guaranteed. Secondly, a static frequency planning scheme that compatible with the characteristics of the BBRS architecture is proposed. Each BS sector can use one half of the total system bandwidth. Furthermore, the soft frequency reuse on FRSs increases the mean data rate of cell edge users and system throughput, so the spectral efficiency is raised. Thirdly, an in-depth analysis of system performance and numerous simulations are carried out, which provides a reference for actual system design. Simulation results illustrate that BBRS architecture achieves a better compromise between performance and complexity.
The rest of the article is organized as follows. The BBRS architecture and corresponding frequency planning scheme are introduced in section II. The CINR performance is analyzed in section III. Rate mapping strategy, path selection and scheduling algorithm are elaborated in section IV. Simulation results are presented in section V. At last, we conclude this article in section VI.
II.BBRS A RCHITECTURE
A.System Model and the BBRS Architecture
The performance of the central cell, i.e., Cell1, is evaluated in a 19-cell OFDMA network, cells marked as (2) to (19) are interfering cells, as shown in Fig. 1. Each cell is divided into S T sectors with M MSs uniformly distributing in each sector, only the handoff in each BS sector is considered throughout this paper. The frame structure for non-transparent relay stations in IEEE 802.16j [2] is adopted, as shown in Fig. 2. We only consider the downlink performance, with AZ and RZ representing the access zone and relay zone in downlink sub-frame. Unitary frequency reuse is employed, and each BS has the same frequency planning. The system works
3
Figure 3. SRS cell architecture and frequency planning.
F r 6
r Figure 4. Main lobe pattern of antennas in BBRS system.
1
Cell (2)
(5)
(8)
(11)
(14)
(17)
(3)
(6)
(9)
(12)
(15)
(18)
(4)
(7)
(10)
(13)
(16)
(19)
Figure 1. 19-cell BBRS cellular network.
under Time Division Duplexing (TDD) with perfect time synchronization.
In the BBRS architecture, each cell is partitioned into six sectors. BS is located in cell center while FRSs, the total number of which in the 19-cell network is 54, are placed on common vertices of the hexagonal cells. Each FRS works under decode-and-forward (DF) mode, and can communicate with three adjacent BSs simultaneously, since equipped with three sector antennas. The total system bandwidth, i.e., BW , is divided into N sub-channels, each of which consists of c adjacent subcarriers. N sub-channels are further divided into 6 orthogonal subsets in the same size, i.e. {6,1,2,...,6}==i i r r N i .
The SRS architecture and corresponding frequency planning scheme [8] is shown as Fig. 3. There are only three FRSs in each cell, so the total number of FRSs in the 19-cell network will be 27.
B. Frequency Planning Scheme in BBRS Architeture
In the BBRS system, the main lobe pattern of the antennas and the frequency planning scheme are depicted as Fig. 4 and Fig. 5, respectively. Each BS sector has two beams, one of which is wider and used for providing coverage to cell center MSs, the other is narrower and used for communicating with the nearest FRS. 1) Frequency Planning at Base Stations
Consider the base station in the central cell, i.e., BS 1. In
AZ, only wide beams are active. Odd sectors, i.e., 13and s 5, reuse sub-channel set b 1={r 1, r 2, r 3}, and even sectors, i.e., s 2, s 4 and s 6 reuse b 2={r 4, r 5, r 6}, as shown in Fig. 4(a). In RZ, both wide and narrow beams are turned on. The frequency planning of wide beams is unchanged, and that of narrow beams is as follows. Odd sectors s 1, s 3 and s 5 reuse b 2={r 4, r 5, r 6}, and even sectors s 2, s 4 and s 6 reuse b 1={r 1, r 2, r 3}, as shown in Fig. 4(b). 2) Frequency Planning at Relay Stations
All FRSs can be classified into two categories, i.e., odd relays and even relays , shared by odd sectors and even sectors of BSs, with F 1 and F 2 as the representatives, respectively, as illustrated in Fig. 4. FRSs of the same category have the same frequency planning.
Relay stations do not transmit in RZ, so only the frequency planning in AZ needs to be considered. As shown in Fig. 4(a), each FRS uses sub-channels that orthogonal with adjacent BS sectors, thus F 1 uses b 2 and F 2 uses b 1. In order to reduce the interference to cell edge users, available sub-channels on each FRS is divided into three parts in the same size, i.e., N /6 sub-channels, and assigned to each sector.
Soft Frequency Reuse (SFR) employs zone-based reuse factors in the cell center and the cell edge areas [10]. Center areas of all cells use the same band with lower transmit power, achieving an efficient use of spectrum resource. Near the cell edge, the sub-channels allocated to adjacent cells are orthogonal and have higher transmit power, so as to control the co-channel interference and guarantee the coverage performance. Inspired by this idea, in order to provide more available sub-channels to relay users, we apply SFR on all FRSs as follows. On the basis of existing frequency planning, each FRS further reuses
Figure 5. Frequency planning scheme in BBRS system.
1122Therefore, the number of available sub-channels on each
FRS sector reaches N /3, and higher cell edge throughput
can be expected.
Finally, the frequency planning at FRSs can be described as follows: three sectors of F 1 use {r 3,r 4}, {r 1,r 5} and {r 2,r 6}, and F 2 allocates {r 5,r 1}, {r 6,r 2} and {r 4,r 3} to
each sector. In each sub-channel set, the transmit power of
the two elements are P low and P h , respectively,
with ≤low h P P and the power ratio ρ=P low /P h .
III. CINR P ERFORMANCE A NALYSIS Assuming all the buffers of MSs are full, all available sub-channels on BSs and FRSs are used up. Interference is in its worst case, and the system performance reaches the lower bound. Equal power allocation strategy is employed, in which the total sector power of BS and FRS is allocated
equally to each sub-carrier. The CINR of the BBRS system will be analyzed first. Only the handoff in each BS sectors is considered, so the analysis of one sector of Cell 1 is enough. In this section, all analyses are based on sector s 1 in Cell 1, which is the area with bold border in Fig. 4(b). According to certain path
selection strategy, MSs access to either BS 1 or F 1, with
corresponding user sets are D ={d m ,m =1,2,…,M 1} and
Q ={q n ,n =1,2,…,M 2}, where M 1+M 2=M .
A. Interference Analysis in AZ
In AZ, user d m in set D suffers interference from all BSs and FRSs. In the BBRS system, N sub-channels are reused
three times and once on BS and FRS, respectively. Average power values of useful signal and the interference from BSs and from FRSs on sub-channel k of d m are:
(1,1,,)(1,1,)=??r B m T m P P G d k A d , (1)
[]19
{1,3,5}1
(,,,)(,,)∈==
???∑∑IBS B
m T m r s b P P
G b s d k A b s d P , (2)
[]1
(,,)(,)==??∑r N IFRS F m T m f P P G f d k A f d , (3) where N r , P B and P F are the total number of FRSs in the system, the transmit power on each subcarrier of BS and FRS, respectively. G (b ,s ,d m ,k ) and G (f ,d m ,k ) are the channel gains from sector s of BS b and FRS f to d m , with
A T (b ,s ,d m ) and A T (f ,d m ) being the antenna gains.
User q n in set Q suffers co-channel interference from all BSs and all FRSs except F 1. Mean power values of useful signal and the interference from BSs and FRSs on sub-channel k of q n are: (1,,)(1,)=??r F n T n P P G q k A q , (4)
[]19
{1,3,5}1{2,4,6}
(,,,)(,,)∈==
??∑∑IBS B
n T n s b or P P
G b s q k A b s q , (5)
[]2
(,,)(,)==??∑r
N IFRS F n T n f P P G f q k A f q . (6) The variable s that stands for co-channel sectors in each cell in (5) will be chosen from {1,3,5} if 1∈k b , otherwise it will be chosen from {2,4,6}.
B. Interference Analysis in RZ
In RZ, only relay station F 1 and users in D are receiving from BS 1.The useful signal of F 1 comes from the narrow beam of s 1, and the interference comes from all BSs. Mean
power of useful signal on sub-channel k of F 1 is:
111(1,1,,)(1,1,)(1,1,)=???r B n Tn R P P G F k A F A F . (7) The average power of interference from wide and narrow beams of all BSs to F 1 is: []19
{2,4,6}1∈==???∑∑IBSwide B T R s b P P G A A , (8) []19{1,3,5}1∈==????∑∑IBSnarrow B n Tn R r s b P P G A A P , (9)
where G =G (b ,s ,F 1,k ) and G n =G n (b ,s ,F 1,k ) are the channel
gains from wide and narrow beam of sector s of BS b to F 1,
with A T =A T (b ,s ,F 1) and A Tn =A Tn (b ,s ,F 1) being the antenna gains, respectively. A R =A R (b ,s ,F 1) is the receiving gain of FRS antenna.
User d m in set D is interfered by all BSs. The mean power of useful signal and interference from wide beams of BSs, i.e., P r and P IBSwide , on sub-channel k of user d m , are
the same as (1) and (2), respectively. The mean power of interference from the narrow beams of BSs is:
[]19
{2,4,6}1
∈==
??∑∑IBSnarrow B
n Tn s b P P
G A , (10)
where G n =G n (b ,s ,d m ,k ) and A Tn =A Tn (b ,s ,d m ) are the channel
gain and antenna gain from the narrow beam of sector s of
BS b to d m , respectively.
In the SRS system, the number of relay stations is 27 in
the 19-cell network, and each BS sector uses N
sub-channels. When variable s in (2) and (5) is chosen from {1,2,3}, and N r in (3) and (6) is 27, (1) to (8) are just the corresponding formulations of the SRS system.
At last, the average CINR on sub-channel k of user u can be expressed as,
TABLE I.
R ELATIONSHIP BETWEEN CINR AND MCS MCS CINR (dB) MCS CINR (dB)
QPSK (1/12) -3.14 16QAM(1/2) 9.94
QPSK (1/6) -0.73 16QAM(2/3) 13.45 QPSK (1/3) 2.09 64QAM(2/3) 18.6
QPSK (1/2) 4.75 64QAM(5/6) 24.58
QPSK (2/3)
7.86
,,ΓΓΓBF min(,)(Γ?Γ?>+BF RZ FM AZ AZ RZ P P P P Figure 6. Path selection strategy.
0(,)=
+?Δr
I P CINR u k P N f
where P r and P I are the mean power of useful signal and the total interference, N 0 and f Δare the AWGN power spectral density and subcarrier spacing, respectively. IV. R ATE M APPING , P ATH SELECTION AND S CHEDULING A. Rate Mapping
In multi-user OFDMA systems, the channel states of different users are fading independently, hence a channel that is in deep fading for user A may be a good channel for user B. When adaptive modulation and coding (AMC) is adopted, better channel state yields higher data rate. If sub-channels are allocated to users with better channel states, then the greater the number of the users is, the higher the throughput is, known as multi-user diversity [10]. When the coding scheme is Convolutional Turbo Code (CTC) and the frame error rate is lower than 10%, the relationship between CINR and the modulation and coding scheme (MCS) is listed in Table I [6].
If M-ary (M=2p ) modulation and the coding with rate a is used in an MCS, then the bits that one subcarrier in an OFDM symbol can carry is ?p a . Assume the channel is stable during a frame, when the mean CINR of a sub-channel is Γ, the corresponding achievable data rate is:
1()Γ=????s F
rate p a c N T , (12)
where T F is the frame length, c and N s are the number of
sub-carriers in a sub-channel and the number of OFDM symbol in each frame, respectively.
B. Path Selection Strategy
In single hop cellular systems, MSs can only access to BSs, thus there is no need for path selection. However, in two hop networks, MSs can access to BSs or FRSs, thus path selection based on channel state is needed. In order to reduce the signaling overhead, the path selection can be carried out by MSs [11]. In the BBRS system, FRSs broadcast the mean CINR of each sub-channel on BS-FRS link, i.e., ΓBF . According to the preamble of BS and FRS, MSs calculate the mean CINR of each sub-channel on BS-MS links and FRS-MS links, i.e., ΓBM and ΓFM .
Based on CINR values obtained and take the bottleneck effect of two hop communications into consideration [6], the pseudocode of the path select strategy can be described in Fig. 6, where P AZ and P RZ are the proportions of AZ and RZ to the frame length.
C. Proportional Fair Scheduling
To maintain low complexity, relay stations usually do not have the ability of scheduling, and all the scheduling is performed by base stations. Assume the access points of users do not change during a frame. Due to different interference states, users may have distinct achievable rates in AZ and RZ. In order to evaluate the system performance more precisely, let BSs allocate resource once in AZ and RZ, respectively. Consider the signaling overhead, BSs may execute scheduling once in a frame in practice. Proportional fair scheduling is considered in this paper, BSs assign a sub-channel to users with the highest
priority at the beginning of each time zone. At time t , the
priority of user u on sub-channel k is:
(,,)
(,,)(,1)
?=
?r u k t u k t R u t , (13)
where r (u,k,t ) is the instantaneous achievable data rate of user u on sub-channel k , (,)R u t is the average obtained data rate in the latest time window with length N W , up to time t , u ∈ {1:M }. Assume the obtained data rate of user u at time t is R (u ,t ), then (,)R u t is updated according to:
11,)(1)(,1)(,)=?
??+?W W
R u t R u t R u t N N . (14) At time t , BS assigns sub-channel k to user:
[]*arg max (,,)?=u
u u k t . (15)
1) Scheduling in BBRS System
In the BBRS system, a BS sector uses two beams, with the same number of sub-channels, i.e., N /2, to send data to
direct users (users that access to BS) and FRS, thus certain fairness between direct users and relay users (users that
access to FRS) is achieved already, and the side effect on
the resource assignment to relay users is eliminated to
some extent. Therefore, it is suitable to schedule direct users and relay users separately.
2) Scheduling in SRS System
TABLE II.
S IMULATION P ARAMETERS
Parameters value Cell radius 1km
Central carrier freq./Bandwidth 2GHz /5MHz
c /N 10/30
Subcarrier spacing f Δ 10.94 kHz Sector power
BBRS: BS/FRS high/low
10/3.3/3.3ρ W SRS: BS/FRS
20/6.6 W
G m : BS(wide/narrow)/FRS 17/21/14 dBi A m : BS(wide/narrow)/FRS
23/27/20 dBi
3dB θ: BS(wide/narrow)/FRS
35/15/70 deg. Number of OFDM symbols in a frame 47 Length of DL sub-frame/UL sub-frame 5/3 Length of DL AZ/ DL RZ 1/1 Pathloss index (LOS/NLOS)
2.35/
3.76 Std. deviation of shadowing (LOS/NLOS)
3/8 dB User velocity
3km/h
In the SRS system, a BS sector only has one beam layer, so direct users and the FRS need to share N sub-channels. The amount of sub-channels that FRS attained in the 1st hop has an important influence on the performance of direct users and relay users, and an appropriate priority value for the FRS is needed.
Consider sector s 1 of BS 1, which is the area with bold border in Fig. 3. Users that access to BS 1 and F 1 are D ={d m ,m =1,2,…,M 1} and Q ={q n ,n =1,2,…,M 2}, respectively, with M 1+M 2=M . Assume the achievable data rates of users in D and Q are r (d m ,k ), m ∈ {1:M 1} and r (q n ,k ), n ∈ {1:M 2}. The average data rate of relay station F 1 can be represented by:
2
11
1(,),)||==∑M n n R F t R q t Q . (16) F 1 use sub-channel set r 3 to serve relay users, which are
users in Q . Sub-channel k is allocated to the user:
[]2{1:}
?()arg max (,)?∈=n n M n
k q k . (17) In order to fully exploit the spectrum resource in the 2nd hop, the channel states of all the relay users must be taken into consideration [12]. Introduce a match factor,
3
?()11(,)(,)β∈=?∑n k k r r q k R F t , (18)
where R (F 1,t ) is the obtained data rate of F 1 at time t , and the 2nd item on the right-hand side is the sum throughput of all relay users. β is updated if F 1 get a sub-channel, and F 1 quits the competition when 1β≤.
If the achievable data rate of F 1 on sub-channel k is r (F 1,k ,t ), then the priority of F 1 is,
111(,,)(,,)(,1)?β=??r F k t F k t R F t . (19) 3) Throughput Direct users can get services in the whole downlink sub-frame, while relay users can only be served in the downlink AZ. Thus the downlink throughput of Cell 1 can be expressed as,
[]12
()1()11(,)(,)(,)T M s AZ
AZ m RZ RZ m S m DL M s s AZ AZ n n P R s d P R s d T P R s q ===???+?+????
=?????????∑∑∑,(20) where S T
, P AZ and P RZ are the number of sectors of Cell 1, the proportions of AZ and RZ to the frame length, respectively. M 1(s ) and M 2(s ) are the number of direct
users and relay users in sector s of Cell 1, R AZ (s
,u ) and R RZ (
s ,u ) are the throughputs of user u in AZ and RZ, respectively. V. N UMERICAL R ESULTS AND D ISCUSSION
In This section, the performance of the BBRS and SRS
system is compared, and main simulation parameters are
listed in table II. Monte Carlo simulation is performed, and
all the results are averaged across 1000 drops. Since the number of sectors of each cell of two systems are 6 and 3,
respectively, so the number of users in each BS sector in SRS system is set to two times of that in BBRS system to
keep the same load. A. Channel Model
Distance based pathloss, lognormal shadowing and small scale fading are taken into consideration.
When carrier frequency is 2GHz, the pathloss is [13]:
128.110lg()()α=+??PL R dB , (21)
where R (in km ) is the distance between source and destination, and α is the pathloss index.
The shadowing effect can be modeled as a variable with normal distribution, S =N (0,σ) (dB ).
The channels between BS and FRSs in the same cell are
considered as in line of sight (LOS) environment, while all the other channels in the system are considered as in non-line of sight (NLOS) environment. The fading under LOS and NLOS can be modeled as Rician and Rayleigh
fading, respectively. Based on the SUI-1 [14] and ITU-Pedestrian A channel model [15], employ the
sum-of-sinusoids simulation model proposed in [16], the two types of fading can be expressed as follows, 1
()exp[(cos )]ωαφ==+p N d n n n Y t j t , (22) 001
()(cos )]exp[(cos )]ωθφωαφ==+++p
d N d n n n Z t j t j t , (23) wher
e N p , ωd , and K are the number o
f propagation paths, the maximum radian Doppler frequency and Rician factor, respectively. (2),1,2,...,απθ=+=n n p p n N n N and φn
Figure 7. CINR distribution in central cell of BBRS (a) and SRS (b).
are the angle of arrival and initial phase of the n th propagation path, 0θ and 0φ are the angle of arrival and the initial phase of the specular component, respectively. φn , θn and 0φ are random variables uniformly distributed over [,)ππ?.
Assume the small scale fading is ()ζdB , and the channel gain is defined by:
0.1()10ζ?++=PL S G . (24)
All MSs use omnidirectional antennas with 0dB gain. BSs and FRSs are equipped with sector antennas with the directional gain model as follows [14],
230.1min 12,()10θθ????????????????
????????????=m m dB G A A , (25) where G m and A m are the maximum gain and the maximum attenuation (also known as the front-to-back ratio), 3dB θis the 3dB beam width, and θ
is the angle between the maximum gain direction of the antenna and the target, respectively.
Assume the transmit power of subcarrier is P , and the power of received signal will be,
()()θθ=???r T T R R P P G A A , (26) where A T (θT ) and A R (θR ) are the transmit and receive antenna gains with θT /θR being the angle between the maximum gain direction of the transmitter/receiver antenna and the receiver/transmitter, respectively. B. CINR Distribution
The numbers of users in each BS sector, i.e., M , in the
SRS and BBRS systems, are set to 600 and 300,
respectively. Only the pathloss is considered. The MCSs
corresponding to the mean CINR across all available sub-channels of all users in the central cell in AZ are recorded. Seven MCSs considered are outage(CINR<-3.14dB ), QPSK(1/12) to QPSK(1/2), QPSK(2/3), 16QAM(1/2), 16QAM(2/3), 64QAM(2/3) and 64QAM(5/6), numbered from 1 to 7, respectively.
Fig. 7 illustrates that, compared with the SRS system,
the outage area is decreased sharply, and better coverage
performance is achieved in the BBRS system. Co-channel
interference is suppressed by the dedicated cell
architecture and frequency planning, thus higher MCSs
can be used by direct users.
C. Multi-user Performance
A multi-user performance metric of relay cellular system, i.e., the combined coverage and capacity index (cc ), is defined by IEEE 802.16j working group [14]:
min 1==
∑k
j j
k
cc R r , (27) where r j is the obtained data rate of user j , and R min is the minimum data rate requirement.
If the total number of users is large, then cc approaches the expected value of the number of users that can be
supported by the system. The cc curve under power ratio ρ＝0.5 and 80% coverage requirement is shown as Fig. 8. We can see that the performance of the BBRS system is
better than the SRS system, when R min changing from 10kbits/s to 200kbits/s.
D. Influence of Non-ideal Characteristics of Antennas
The non-ideal characteristics of the sector antennas have significant influence on system throughput. Raise the
maximum attenuation, i.e., A m , of the two systems in step of 3dB for 4 times, the same analysis is conducted for the
maximum gain G m as well. The throughput performance is
shown as Fig. 9. With the increasing of A m , the interfe-rence to other directions is reduced, and the throughputs of two systems both rise. However, the influence of G m
is
quite different from A m . In the SRS system, the raise of G m
reduces the proportion of the outage area, achieving a
higher throughput. But in the BBRS system, a higher coverage percentage has already achieved, the raise of G m
causes greater co-channel interference, resulting in lower
throughput.
E. Influence of Frequency Reuse Soft frequency reuse is considered in the proposed BBRS system. The coverage of the FRSs and system throughput will be affected if the power ratio ρ is changed. When the total number of users in Cell 1
is set to
60, 120, 180, 240 and 300, and the power ratio ρis set to
0，0.25 and 1, the throughput performance of Cell 1 is
shown as Fig. 10. Due to the multi-user diversity, the
M e a n c e l l t h r o u g h p u t (M b i t s /s )
Figure 9. Influence of antenna parameters to throughput. 1002003004005001820222426283032ρ=0.25ρ=1.0
ρ=0bigger the number of users is, the higher the throughput is. The growth of the throughput slows down with the in-creasing of the power ratio. A good compromise is achieved between the throughput and the power con-sumption when ρ=0.25, compared with ρ=0, i.e., the scenario with no soft frequency reuse on FRSs.
The available number of sub-channels for each BS sector in the BBRS system is only one half of that in the SRS system, which may result in lower throughput. However, due to the effectiveness of interference mitigation, higher throughput can be expected. It can be seen clearly from Fig. 10 that, the performance improvement of the BBRS system is noticeable. There is an increase about 27%~34% over the SRS system, even though no soft frequency reuse on FRSs is considered.
The results upon imply that more available sub-channels do not represent higher throughput, for the co-channel interference has an important influence on the performance. When there are no relay stations, the co-channel interference is reduced further. The throughputs of the SRS and BBRS systems raise about 11% to 12% and decrease about 11% to 19%. However, the latter is still higher than the former, which demonstrates that the frequency planning performance of the manner with orthogonal sub-channels assigned to adjacent sectors in the same cell is better than that of the
aggressive frequency reuse in which all sectors using the whole system band.
F. The Performance of Direct Users and Relay Users One of the main roles of relay stations in relay cellular systems is to improve the data rates of cell edge users. As a relay network, cell edge performance of the proposed BBRS system needs to be evaluated.
As shown in Fig. 11, compared with the SRS system, in
the BBRS system, when ρ
=0.25, not only does the average data rate of relay users increase by five to eight times but also that of direct users rises slightly. Furthermore, compared with ρ=0, when ρ=0.25, due to more serious intra-cell interference, the performance of direct users deceases, but that of relay users increases, for more sub-channels is available. Therefore, a compromise between the performance of direct users and relay users needs to be considered when choosing the parameter ρ.
VI. C ONCLUSION
In this paper, a bilayer beams and relay sharing based (BBRS) OFDMA cellular architecture and corresponding frequency planning scheme are proposed. From the simulation results we can conclude that, sector antennas can suppress interference in OFDMA cellular systems efficiently, and the aggressive frequency reuse without considering the co-channel interference will result in lower system performance.
Due to the spectrum resource is limited, the growing demand for higher data rate makes it necessary to consider tighter frequency reuse, where co-channel interference is more serious and a higher requirement for interference suppression is needed. In order to solve this problem, several techniques can be considered. Firstly, in the proposed BBRS system, the shared relay stations provide a convenient way for local interference coordination, in which the main interference can avoid and a substantial performance improvement can be expected. Secondly, cooperation between base stations and relay stations may improve cell edge users’ performance further. Thirdly, a better performance can be expected if dynamic frequency planning is employed when cell load changes fast. All the
aspects mentioned above will be included in our future work.
A CKNOWLEDGMENT
The authors wish to thank the anonymous reviewers for their constructive comments that have improved the quality of this paper.
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Yanxiong Pan was born in 1982. He received his
B.S. degree in Space Tracking Telemetry and
Command from Academy of Equipment Command &
Technology of P.L.A., Beijing, China, in 2004. Since
2008, he has been working toward the M.S. degree in
Electrical Engineering at University of Science and
Technology of China, Hefei, China.
He was an engineer at Yibin Tracking Telemetry
Station, Xichang Satellite Launch Center, Yibin, China, from 2004 to 2008. His current research interests include radio resource
management and relay communication.
Hui Han
received the B.S. degree from Chongqing
Communication Institute of P.L.A., in 2002, and the
M.S. degree in Electrical Engineering from University
of Science and Technology of China, Hefei, China, in
2009.
He is currently a lecturer in the department of Information Engineering, Chongqing Communication
Institute of P.L.A. His research interests include error
control coding and wireless communication.
Sihai Zhang received the B.S. degree in Computer
Science (CS) from Ocean University of China, in 1996,
and the M.S. and Ph.D. degrees in CS from University
of Science and Technology of China (USTC), Hefei,
China, in 2002 and 2006, respectively.
He is currently a lecturer in the department of
Electronic Engineering and Information Science,
USTC. His research interests include evolutionary computation, wireless communication network, and social network.
Wuyang Zhou received his B.S. and M.S. degrees
from Xidian University, Xi’an, China, in 1993 and
1996, respectively, and Ph.D. degree in Electrical
Engineering from University of Science and
Technology of China (USTC), Hefei, China, in 2000.
He is currently a professor in the department of
Electronic Engineering and Information Science,
USTC. His research interests include error control
coding, radio resource allocation, and wireless
networking.
继电器的基本知识
继电器的定义、分类、命名 一、继电器的定义 1、继电器的定义 继电器:当输入量(或激励量)满足某些规定的条件是能在一个或多个电器输出电路中产生跃变的一种器件 2、继电器的继电特性 继电器输出入量和输出量之间在整个变化过程中的相互关系成为继电器的继电特征或控制特征.用x表示输入回路量,y表示输出回路的输出量,如图1所示.当输出量x 连续变化到一定量xa时,输出量y发生跃变,有0增加到ya值,则是输入量继续增加,是输出保持不变.相反,当减少到xb是,y又突然由ya减少到0.xa被称为继电器的动作值,xb被称为继电器的释放值,ya即是继电器的负载. 二、继电器的分类 1、按继电器的工作原理或结构特征分类 （1）电磁继电器：利用输入电路内点路在电磁铁铁芯与衔铁间产生的吸力作用而工作的一种电气继电器。 直流电磁继电器：输入电路中的控制电流为直流的电磁继电器。 交流电磁继电器：输入电路中的控制电流为交流的电磁继电器。 磁保持继电器：利用永久磁铁或具有很高剩磁特性的铁芯，是电磁继电器的衔铁在其线圈断点后仍能保持在线圈通电时的位置上的继电器。 （2）固体继电器：指电子元件履行其功能而无机械运动构件的，输入和输出隔离的一种继电器。 （3）温度继电器：当外界温度达到给定值时而动作的继电器。 （4）舌簧继电器：利用密封在管内，具有触电簧片和衔铁磁路双重作用的舌簧的动作来开,闭或转换线路的继电器。 干簧继电器：舌簧管内的介质的介质为真空，空气或某种惰性气体，即具有干式触点的舌簧继电器。 湿簧继电器：舌簧片和触电均密封在管内，并通过管底水银槽中水银的毛细作用，而使水银膜湿润触点的舌簧继电器。 剩簧继电器：由剩簧管或有干簧关于一个或多个剩磁零件组成的自保持干簧继电器。 舌簧管：同理舌簧管有干簧管,湿簧管,剩簧管三种类型。 （5）时间继电器：当加上或除去输入信号时，输出部分需延时或限时到规定的时间才闭合或断开其被
继电器分类
继电器的分类方式较多，可以按结构、外形尺寸、功耗等来分。从功能特征分，我公司的继电器主要包括： 电磁继电器——是一种单稳态继电器，也是一种用量最大的继电器。线圈在规定的激励量作用下，其输出状态改变，但在激励撤消后，输出状态复原到初始状态。 磁保持继电器——是一种双稳态继电器。线圈在规定的激励量作用下其输出状态改变，但在激励撤消后，能保持已有状态。 温度继电器——是一种温度敏感元件，它的输出状态完全由所需控制的温度高低决定。 时间继电器——当继电器输入发生变化而输出响应并不同步发生而是按规定延迟的继电器。 高频继电器——传输高频信号并具有传输损耗最小的继电器，如射频同轴继电器。 特种继电器——是专为某一物理量的变化而设计的继电器。其输出状态完全由这一物理量的量值决定。比如反映气体流量的风速继电器等。 1 电磁继电器 动作值（吸合值）、保持值、释放值的检测程序:检测程序如图1,按GJB65B等国军标的规定，图1a、图1b所示的两种检测方法都有效；图1a为渐变电压检测法，该方法检测值重现性好，被广为采用，但这并不表示使用时要先磁化后工作。图1b为阶跃函数电压检测法。 2 磁保持继电器 动作值的检测:动作值（无释放值）的检测可参照图1a的渐变电压检测法；同样也可采用图2的阶跃函数电压检测法，首先给1号线圈（后激励线圈，产品标准和样本中有标注）加规定的激励量，检查其输出状态应符合继电器电路图给出的后激励输出状态，此动作电压值亦称为自保持值；反之当2号线圈激励时的动作电压值也称为复归值。
3 温度继电器 3. 1 温度特性（动作温度、动作温度偏差、回复温度、回复温度范围） a. 动作温度（又称高温整定值）：继电器按规定的升温速度升温而发生输出状态变化时的温度值； b. 标称动作温度：无动作温度偏差的的动作温度值，如50±3℃中的50℃； c. 动作温度偏差：实测动作温度与标称动作温度的差值，如50±3℃中的±3℃范围； d. 回复温度（又称低温整定值）：继电器按a条的要求动作后，按规定降温速度降温而发生输出状态变化时的温度值； e. 回复温度范围：继电器动作温度与回复温度的差值，由产品标准或用户作出规定。 3.2 温度继电器温度特性的检测方法 温度继电器的检测方法有三种，而三种都被认为是有效的。这三种方法是：试块测定法，空气测定法，液体测定法。 a. 试块测定法：是指在室温下，将产品感温面紧贴在一被加热的金属块上（通常为铜块）通过检测金属块的温度来确定继电器的温度特性。 b. 空气测定法：是指将产品置于有空气循环装置的烘箱内进行检测。 c. 液体测定法：是指将产品置于有液体循环装配的槽液中进行检测。 以上三种方法对同一产品的检测结果是有差异的。公司广为采用的是试块测定法和空气测定法。另外产品检测中的升降温速度对检测结果也影响大，必须严格按标准的规定来选择升降温速度。为保证使用要求，供需双方应即时沟通修正产品的温度特性具体的温度特性描述见图3。
继电器的结构和工作原理及应用举例
继电器的结构和工作原理及其在电机控制中的应用举例 一、继电器的结构和工作原理 图l-2a是继电器结构示意图，它主要由电磁线圈、铁心、触点和复位弹簧组成。继电器有两种不同的触点，于断开状态的触点称为常开触点(如图1-2中的触3，4)，处于闭合状态的触点称为常闭触点(如图1-2中的触点当线圈通电时，电磁铁产生磁力，吸引衔铁，使常闭触点断开，常开触点闭合。线圈电流消失后，复位弹簧的位置，常开触点断开，常闭触点闭合。图l-2b是继电器的线圈、常开触点和常闭触点在电路图中的符号。一若干对常开触点和常闭触点。在继电器电路图中，一般用相同的由字母、数字组成的文字符号(如KA2)来标注同圈和触点。
二、接触器在电机控制中的应用 图1—3是用交流接触器控制异步电动机的主电路、控制电路和有关的波形图。接触器的结构和工作原理与继电区别仅在于继电器触点的额定电流较小，而接触器是用来控制大电流负载的，例如它可以控制额定电流为几十安电动机。按下起动按钮SBl，它的常开触点接通，电流经过SBl的常开触点和停止按钮SB2、作过载保护用的热闭触点，流过交流接触器KM的线圈，接触器的衔铁被吸合，使主电路中的3对常开触点闭合，异步电动机M 通，电动机开始运行，控制电路中接触器KM的辅助常开触点同时接通。放开起动按钮后，SBl的常开触点断开辅助常开触点和SB2、FR的’常闭触点流过KM的线圈，电动机继续运行。KM的辅助常开触点实现的这种功或“自保持”，它使继电器电路具有类似于R-S触发器的记忆功能。 在电动机运行时按停止按钮SB2，它的常闭触点断开，使KM的线圈失电，KM的主触点断开，异步电动机断，电动机停止运行i同时控制电路中KM的辅助常开触点断开。当停止按钮SB2被放开，其常闭触点闭合后，失电，电动机继续保持停止运行状态。图1.3给出了有关信号的波形图，图中用高电平表示1状态(线圈通电、低电平表示0状态(线圈断电、按钮被放开)。 图1.3中的控制电路在继电器系统和PLC的梯形图中被大量使用，它被称为“起动-保持-停止”电路，或简称路。
中间继电器
DZ-3/Z系列中间继电器 1 用途 DZ-3/Z系列中间继电器用于直流操作的各种保护和自动控制中，作为辅助继电器以增加触点数量和触点容量。 2 结构和工作原理 继电器为电磁式继电器。采用JK-1型壳体，将DZY-200机芯装入壳体中，具有透明的壳罩可以清楚观察到继电器的内部结构。外形尺寸及开孔图见附图。 当电压加到线圈两端时，衔铁向闭合位置运动，此时动合触点闭合，动断触点断开。断开电源时，衔铁在触点片的压力作用下，返回到原始状态，动合触点断开，动断触点闭合。内部接线图见图1。 3 技术要求 3.1 继电器的额定技术数据及触点形式 表1 型号规格直流额定电压(V) 触点形式及数量 动合动断 DZ-3/Z1 220 110 48 24 2 6 DZ-3/Z2 4 4 DZ-3/Z3 6 2 DZ-3/Z4 - 8 DZ-3/Z5 8 - 3.2 动作电压：不大于额定电压的70%，不小于额定电压30%。 3.3 返回电压：不小于额定电压的5%。 3.4 动作时间：在额定电压下不大于0.05s。 3.5 功率消耗：在额定电压下不大于5W。
图1 内部接线图(正视) 4 调试方法 4.1 触点间隙：动合触点不小于1.5mm,动断触点不小于1mm，触点超行程不小于0.3mm。 4.2 调整触点片压力可以改变动作值和返回值。
DZ-30B系列中间继电器 1 用途 DZ-30B 系列中间继电器用于直流操作的各种保护和自动控制线路中，作为辅助继电器以增加触点数量和触点容量。 2 结构和工作原理 继电器为电磁式动作继电器。采用JK-1型壳体，将DZY-200机芯装入壳体中，具有透明的壳罩可以清楚观察到继电器的内部结构。外形尺寸及开孔图见附图。当电压加在线圈两端时，衔铁向闭合位置运动，此时动合触点闭合，动断触点断开。断开电源时，衔铁在接触片的压力作用下，返回到原始状态，动合触点断开，动断触点闭合。内部接线图见图1。 3 技术要求 3.1 继电器的额定技术数据及触点形式 型号触点形式直流额定电压(V) DZ-31B 三动合三转换 220，110，48，24，12 DZ-32B 六动合 3.2 动作电压：不大于额定电压的70%，不小于额定电压的30%。 3.3 返回电压：不小于额定电压的5%。 3.4 动作时间：在额定电压下不大于0.05s。 3.5 功率消耗：在额定电压下不大于5W。 4 调试方法 4.1 触点间隙，动合触点不小于1.5mm，动断触点不于小1mm。触点超行程不小于0.3mm。 4.2 调整触点片的压力可以改变动作值和返回值。
继电器分类及原理
继电器是什么? 继电器是一种电子控制器件，它具有控制系统(又称输入回路)和被控制系统(又称输出回路)。它实际上是用较小的电流去控制较大电流的一种“自动开关”。 继电器的分类： 1、按工作原理和结构特性可分为：电磁继电器、固体继电器、温度继电器、舌簧继电器、时间继电器、高频继电器、极化继电器、其他类型的继电器（有继电器，声继电器，热继电器，仪表式继电器，霍尔效应继电器，差动继电器等） 2、按动作原理可分为：电磁型、感应型、整流型、电子型、数字型等 3、按继电器的作用可分为：启动继电器、量度继电器、时间继电器、中间继电器、信号继电器、出口继电器 一、电磁继电器的工作原理和特性
电磁式继电器一般由铁芯、线圈、衔铁、触点簧片等组成的。只要在线圈两端加上一定的电压，线圈中就会流过一定的电流，从而产生电磁效应，衔铁就会在电磁力吸引的作用下克服返回弹簧的拉力吸向铁芯，从而带动衔铁的动触点与静触点(常开触点)吸合。当线圈断电后，电磁的吸力也随之消失，衔铁就会在弹簧的反作用力返回原来的位置，使动触点与原来的静触点(常闭触点)吸合。这样吸合、释放，从而达到了在电路中的导通、切断的目的。对于继电器的“常开、常闭”触点，可以这样来区分：继电器线圈未通电时处于断开状态的静触点，称为“常开触点”;处于接通状态的静触点称为“常闭触点”。 固态继电器的原理及结构 SSR按使用场合可以分成交流型和直流型两大类，它们分别在交流或直流电源上做负载的开关，不能混用。 下面以交流型的SSR为例来说明它的工作原理，图1是它的工作原理框图，图1中的部件①-④构成交流SSR的主体，从整体上看，SSR只有两个输入端(A和B)及两个输出端(C和D)，是一种四端器件。 图1 工作时只要在A、B上加上一定的控制信号，就可以控制C、D两端之间的“通”和“断”，实现“开关”的功能，其中耦合电路的功能是为A、B端输入的控
安全继电器工作原理
安全继电器工作原理 关于安全继电器工作原理，实际上存在两个层面问题：一是未能区分安全继电器与普通继电器的区别。二是不清楚安全继电器如何搭建形成的安全继电器模块。大家想了解安全继电器工作原理，其实真正同应用相关的的是安全继电器模块的工作原理！基于当前安全设计在国内尚处于刚刚有所需求的实际情况，工程师无论是对安全继电器，还是安全继电器工作原理都不是特别清楚，为了更好服务设计工作，天之行愿就安全继电器工作原理同广大设计人员进行相关的交流。 第一个问题：安全继电器元件是如何构建安全继电器模块的，涉及安全继电器与普通继电器的区别 第二个问题：安全继电器工作原理才是我们搭建安全回路时，真正需要知道的！ 下面我们将从三个方面予以介绍： 一、功能作用—解决什么问题？ 在设备运行过程中，由于外部的原因，或者违规操作（无论是不懂导致的误动作或是疲劳导致的误动作），以及内部器件失效，都可能导致事故的出现，轻则财物损失，重则发生机毁人亡的恶性事故，为了降低这些事故的出现，我们在进行这些设备的设计时，一般都会针对相关情况做出相应的安全设计：如急停设计、安全门设计、安全光幕设计，双手启动设计，安全边沿设计等。这些设计要时刻实现相应的安全功能，必须基于所有的器件都能保持动作正常，功能完好！ 显然这是一种理想状态，真实的情况是：从来没有“不坏”的器件，总是有一些器件在运行中会出现这样或那样的异常，导致其功能出现故障。这样由于
某个器件出现了故障，将会导致设计中整个安全功能的丧失，从而使得事故发生的概率大幅度的提高！ 举个例子：当周围环境出现了状况，你希望急停设计启动，断电停机！当你拍下急停按钮时，由于种种原因，按钮卡阻了，接入电路中的常闭触点未能分开，自然也就无法实现断电停机----急停安全设计完全失效！又或者，当你拍下急停按钮后，急停按钮没有问题，接主电源的交流接触器发生了触头粘连，不能断开，此时你当然无法实现断电停机----急停安全设计完全失效！ 在上述举例中，我们发现，任一个器件的功能异常，就可以导致整个安全设计的丧失！也许有人会说，选高品质的器件就可以解决这个问题!是的，没错，提高器件品质永远是降低事故的一个不二选择！然而，品质提高永远在路上。如何在当下现实的器件品质水平下，可靠维持安全设计功能的实现，从而降低事故发生的概率就成了一个必须解决的问题！也就是说，如何在承认器件可能存在故障的前提下，任然能维持系统安全功能不丧失，且故障能被及时检查出来！安全继电器原理就是为解决此问题而被发明出来的一个功能器件。 二、安全继电器模块动作逻辑
热继电器的结构及工作原理
热继电器是一种应用比较广泛的保护继电器，具有反时限的保护特性。 热继电器是依靠电流通过发热元件时所产生的热量，使双金属片受热弯曲而推动机构动作的一种电器。主要用于电动机的过载保护断相及电流不平衡运行的保护及其他 电气设备发热状态的控制。 热继电器的分类 热继电器的型式有许多种，其中常用的有： 双金属片式：利用双金属片用两种膨胀系数不同的金属，通常为锰镍铜板轧制成受热弯曲去推动杠杆而使触头动作。 热敏电阻式：利用电阻值随温度变化而变化的特性制成的热继电器。 易熔合金式：利用过载电流发热使易熔合金达到某一温度值时，合金熔化而使继电器动作。 作为电气设备主要是电动机过载保护用的热继电器种类虽很多，但使用得最多最普遍的还是双金属片式热继电器。它具有结构简单体积较小成本较低以及在选用适当的热元件的基础上能够获得较好的反时限保护特性等优点。目前，我国生产的热继电器都是双金属片式，它常与接触器组合成电磁启动器。它可按下述方法分类。 按极数分：有单极双极和三极。其中三极的又包括带有断相保护装置的和不带断 相保护装置的。 按复位方式分：自动复位触头断开后能自动返回到原来位置和手动复位。 按电流调节方式分：电流调节和无电流调节借更换热元件来达到改变整定电流的。 按温度补偿分：有温度补偿和无温度补偿。 按控制触点分：带常闭触点触点动作前是闭合的带常闭和常开触点。触点的结构形式有：转换触点桥式双断点等。
热继电器的结构及工作原理 热继电器是用于电动机或其它电气设备、电气线路的过载保护的保护电器。电动机在实际运行中，如拖动生产机械进行工作过程中，若机械出现不正常的情况或电路异常使电动机遇到过载，则电动机转速下降、绕组中的电流将增大，使电动机的绕组温度升高。若过载电流不大且过载的时间较短，电动机绕组不超过允许温升，这种过载是允许的。但若过载时间长，过载电流大，电动机绕组的温升就会超过允许值，使电动机绕组老化，缩短电动机的使用寿命，严重时甚至会使电动机绕组烧毁。所以，这种过载是电动机不能承受的。热继电器就是利用电流的热效应原理，在出现电动机不能承受的过载时切断电动机电路，为电动机提供过载保护的保护电器。 热继电器工作原理示意图如图1 图1 热继电器工作原理示意图 1——热元件，2——双金属片，3——导板，4——触点 热继电器的结构如图2所示。 图1 热继电器结构示意图 图中：1——电流调节凸轮，2——片簧（2a，2b），3——手动复位按钮，4——弓簧片，5——主金属片，6——外导板，7——内导板，8——常闭静触点，9——动触点，10——杠杆，11——常开静触点（复位调节螺钉），12——补偿双金属片，13——推杆，14——连杆，15——压簧 使用热继电器对电动机进行过载保护时，将热元件与电动机的定子绕组串联，将热继电器的常闭触头串联在交流接触器的电磁线圈的控制电路中，并调节整定电流调节旋钮，使人字形拨杆与推杆相距一适当距离。当电动机正常工作时，通过热元件的电流即
高压继电器知识大全
高压继电器*概述 压继电器，用于交直流操作的各种保护和自动控制装置中以增加触点的数量及容量。部分型号增加一副带机械保持的动合信号触点并带有动作信号指示器。高压继电器均采用空气绝缘式绝缘负载、安全泄量与安全接地，符合OSHA及其它安全标准，且在高压、大电流等苛刻条件下仍具有常规继电器所无法比拟的可靠性及使用寿命长等特点，被广泛应用于不同领域，包括医疗仪器(心脏起搏器、肾结石排除装置、核磁共振成像)、航空和军用设备(高频天线耦合装置、多路模式雷达、激光测距仪、空间和卫星应用、闪电保护)、商业应用(电动车辆和快速运输、海底电缆分叉系统、科学和检测设备、深井油田应用、电池备份和不间断电源系统)。 高压继电器*结构 典型的高压继电器包含四个基本部分： 密封的灭弧室，接触点位于灭弧室内部，达到耐高压的目的; 带动动触点运动的衔铁机构; 提供动力的线圈部分; 便于使用方安装与连接的附加部分。 高压继电器*工作原理 当继电器线圈施加激励量等于或大于其动作值时衔铁被吸向导磁体同时衔铁压动触点弹片使触点接通、断开或切换被控制的电路。当继电器的线圈被断电或激励量降低到小于其返回值时衔铁和接触片返回到原来位置。 高压继电器*介质 高压直流继电器主要采用两种不同的介质，一种是真空介质，另一种是高压气体介质。 真空介质的特点： 由于在真空中只有非常少的气体分子，这使得真空中不容易产生电弧，在理想的状态下，真空有可能达到每0.1毫米10000V的介电强度。另外，由于没有空气的存在，真空中触点不会氧化，因此真空型继电器的接触电阻较小而且较稳定。特别适合应用于射频场合。 高压气体介质的特点： 纯净的高压气体介质能使继电器保持良好的耐压并保护触点不被氧化，它在继电器进行热开关时可以避免触点高温烧损。这种继电器用于ESD测试设备、电缆测试设备和心脏起搏器，是理想的电容器快速充电或放电的开关元件。在对电流波动很敏感的应用中，充气继电器具有低而稳定的泄漏电流，特别是在断开触点间，可以长时间保持很低的泄漏电流
各种继电器图形符号及其作用、特点
继电器 在机电控制系统中，虽然利用接触器作为电气执行元件可以实现最基本的自动控制，但对于稍复杂的情况就无能为力。在极大多数的机电控制系统中，需要根据系统的各种状态或参数进行判断和逻辑运算，然后根据逻辑运算结果去控制接触器等电气执行元件，实现自动控制的目的。这就需要能够对系统的各种状态或参数进行判断和逻辑运算的电器元件，这一类电器元件就称为继电器。 继电器实质上是一种传递信号的电器，它是一种根据特定形式的输入信号转变为其触点开合状态的电器元件。一般来说，继电器由承受机构、中间机构和执行机构三部分组成。承受机构反映继电器的输入量，并传递给中间机构，与预定的量（整定量）进行比较，当达到整定量时（过量或欠量），中间机构就使执行机构动作，其触点闭合或断开，从而实现某种控制目的。 继电器作为系统的各种状态或参量判断和逻辑运算的电器元件，主要起到信号转换和传递作用，其触点容量较小。所以，通常接在控制电路中用于反映控制信号，而不能像接触器那样直接接到有一定负荷的主回路中。这也是继电器与接触器的根本区别。 继电器的种类很多，按它反映信号的种类可分为电流、电压、速度、压力、温度等；按动作原理分为电磁式、感应式、电动式和电子式；按动作时间分为瞬时动作和延时动作。电磁式继电器有直流和交流之分，它们的重要结构和工作原理与接触器基本相同，它们各自又可分为电流、电压、中间、时间继电器等。下面介绍几种常用的继电器。 1. 中间继电器 中间继电器是用来转换和传递控制信号的元 件。他的输入信号是线圈的通电断电信号，输 出信号为触点的动作。它本质上是电压继电 头能承受的电流较大（额定电流5A～10A）、 动作灵敏（动作时间小于0.05s）等特点。中 间继电器的图形符号如图6.28所示，其文字 符号用KA表示。 中间继电器的主要技术参数有额定电压、额定 电流、触点对数以及线圈电压种类和规格等。
继电器的特性和类型
继电器的特性和类型 继电器属于一种微电控制器件，在电路中起着自动调节安全保护转换电路等作用。 1、电磁式电磁继的工作原理： 电磁式继电器一般由铁芯、线圈、衔铁、触点簧片等组成的。只要在线圈两端加上一定的电压，线圈中就会流过一定的电流，从而产生电磁效应，衔铁就会在电磁力吸引的作用下克服返回弹簧的拉力吸向铁芯，从而带动衔铁的动触点与静触点（常开触点）吸合。当线圈断电后，电磁的吸力也随之消失，衔铁就会在弹簧的反作用力返回原来的位置，使动触点与原来的静触点（常闭触点）吸合。这样吸合、释放，从而达到了在电路中的导通、切断的目的。对于继电器的“常开、常闭”触点，可以这样来区分：继电器线圈未通电时处于断开状态的静触点，称为“常开触点”；处于接通状态的静触点称为“常闭触点”。 2、热敏干簧继电器的工作原理： 热敏干簧继电器是一种利用热敏磁性材料检测和控制温度的新型热敏开关。它由感温磁环、恒磁环、干簧管、导热安装片、塑料衬底及其他一些附件组成。热敏干簧继电器不用线圈励磁，一般称为热敏开关。而由恒磁环产生的磁力驱动开关动作。恒磁环能否向干簧管提供磁力是由感温磁环的温控特性决定的。 3、固态继电器SSR的工作原理： 一般使用于禁止电火花的地方，固态继电器是一种两个接线端为输入端，另两个接线端为输出端的四端器件，中间采用隔离器件实现输入输出的电隔离。固态继电器按负载电源类型可分为交流型和直流型。按开关型式可分为常开型和常闭型。按隔离型式可分为混合型、变压器隔离型和光电隔离型，以可控硅和光电隔离型为最多。 国内表达继电器的符号和触点方法 继电器线圈在电路中用一个长方框符号表示，如果继电器有两个线圈，就画两个并列的长方框。同时在长方框内或长方框旁标上继电器的文字符号“J”。继电器的触点有两种表示方法：一种是把它们直接画在长方框一侧，这种表示法较为直观。另一种是按照电路连接的需要，把各个触点分别画到各自的控制电路中，通常在同一继电器的触点与线圈旁分别标注上相同的文字符号，并将触点组编上号码，以示区别。继电器的触点有下面几种基本形式： A.动合型：H型；线圈不通电时两触点是断开的，通电后，两个触点就闭合。以合字的拼音字头“H”表示。 B.动断型：D型；线圈不通电时两触点是闭合的，通电后两个触点就断开。用
固态继电器工作原理解析
固态继电器工作原理解 析 Document number：PBGCG-0857-BTDO-0089-PTT1998
杭州国晶 固态继电器(SSR)与机电继电器相比，是一种没有机械运动，不含运动零件的继电器，但它具有与机电继电器本质上相同的功能。SSR是一种全部由固态电子元件组成的无触点开关元件，他利用电子元器件的点，磁和光特性来完成输入与输出的可靠隔离，利用大功率三极管，功率场效应管，单项可控硅和双向可控硅等器件的开关特性，来达到无触点，无火花地接通和断开被控电路。 固体继电器的工作原理 固体继（SolidStateRelaySSR)是利用现代微电子技术与电力电子技术相结合而发展起来的一种新型无触点电子开关器件。它可以实现用微弱的控制信号(几毫安到几十毫安)控制0．1A直至几百A电流负载，进行无触点接通或分断。固体继是一种四端器件，两个输入端，两个输出端。输入端接控制信号，输出端与负载、串联，SSR实际是一个受控的电力电子开关，其等效电路如图。
由于固体继具有高稳定、高可靠、无触点及寿命长等优点，广泛应用在电动机调速、正反转控制、调光、家用、烘箱烘道加温控温、送变电电网的建设与改造、电力拖动、印染、塑科加工、煤矿、钢铁、化工和军用等方面。 固体继的工作原理 固体继与通常的电磁继不同：无触点、输入电路与输出电路之间光(电)隔离、由分立元件．半导体微电子电路芯片和电力电子器件组装而成，以阻燃型环氧树脂为原料，采用灌封技术持其封闭在外壳中、使与外界隔离，具有良好的耐压、防腐、防潮抗震动性能。 固体继由输入电路、驱动电路和输出电路三部分组成。 这里仅以应用较多的交流过零型固体继为例，介绍其工作原理。该电路采用了过零触发技术，具有电压过零时开启，负裁电流过零时关断的特性，在负载上可以得到一个完整的正弦波形，因此电路的射频干扰很小。 该 电路由 信号输
继电器的工作原理和作用
继电器的工作原理 简介 当输入量(如电压、电流、温度等)达到规定值时，使被控制的输出电路导通或断开的电器。可分为电气量(如电流、电压、频率、功率等)继电器及非电气量(如温度、压力、速度等)继电器两大类。具有动作快、工作稳定、使用寿命长、体积小等优点。广泛应用于电力保护、自动化、运动、遥控、测量和通信等装置中。 1、电磁继电器的工作原理和特性 电磁式继电器一般由铁芯、线圈、衔铁、触点簧片等组成的。只要在线圈两端加上一定的电压，线圈中就会流过一定的电流，
从而产生电磁效应，衔铁就会在电磁力吸引的作用下克服返回弹簧的拉力吸向铁芯，从而带动衔铁的动触点与静触点（常开触点）吸合。当线圈断电后，电磁的吸力也随之消失，衔铁就会在弹簧的反作用力返回原来的位置，使动触点与原来的静触点（常闭触点）释放。这样吸合、释放，从而达到了在电路中的导通、切断的目的。对于继电器的“常开、常闭”触点，可以这样来区分：继电器线圈未通电时处于断开状态的静触点，称为“常开触点”；处于接通状态的静触点称为“常闭触点”。 继电器的输入信号x从零连续增加达到衔铁开始吸合时的动作值xx,继电器的输出信号立刻从y=0跳跃到y=ym,即常开触点从断到通。一旦触点闭合，输入量x继续增大，输出信号y将不再起变化。当输入量x从某一大于xx值下降到xf,继电器开始释放，常开触点断开。我们把继电器的这种特性叫做继电特性，也叫继电器的输入-输出特性。 释放值xf与动作值xx的比值叫做反馈系数，即 Kf= xf /xx 触点上输出的控制功率Pc与线圈吸收的最小功率P0之比叫做继电器的控制系数，即Kc=PC/P0 2、热敏干簧继电器的工作原理和特性 热敏干簧继电器是一种利用热敏磁性材料检测和控制温度的新型热敏开关。它由感温磁环、恒磁环、干簧管、导热安装片、塑料衬底及其他一些附件组成。热敏干簧继电器不用线圈励磁，
步进继电器的结构及工作原理
步进继电器的结构及工作原理 步进继电器的内部结构如图所示。它由线圈、衔铁、推动杆、棘轮、棘爪及触点等组成。它的棘轮有三层，中间一层是作步迸运动用的。 当线圈通以电流时，线圈便产生磁场，从而使衔铁在电磁吸力的作用下吸向铁心，此时衔铁带动推杆使中间棘轮逆时针转动一步，于是上、下两层棘轮便板簧移动。由于触点是和板簧固定在起的，所以板簧的移动就会使上、下两层触点改变接触状态。当驱动电脉冲消失后，线圈失去电流，电磁吸力也随之消失，衔铁在恢复弹簧的作用下恢复到初始状态，此时棘几顶住秧轮上的齿面不让棘轮发生转动，起到了定位的作用，因此触点方能保持状态不变。只要改变上、下两层棘轮的齿数和齿形，便可得到1~2个触点、2~4个步序为一个循环的、具有不同控制功能的产品系列。 BT系列步进继电器是台湾和可公司的专利产品，具有以下特点：1：不需要维持电流，具有自锁功能。BF系列步进继电器用脉冲触发动作，当触发脉冲电流消失后，由机械结构保持触点的状态，以后每来一个脉冲，机构就跳转一步，是触点改变一次状态。2：有简单的编程功能。BF系列步进继电器有单触点和双触点两大类。对双触点继电器来讲，他的触点可有2得2次方个状态。将这些不同的状态按不同次序排列，可生产出多种不
同的产品。3：品种多样自成系列。（1）有螺钉安装和轨道安装两种。（2）工作电压，直流产品有12伏和24伏两种。交流产品有12伏，24伏，110伏，120伏，220伏，230伏和240伏共七种。4功能多样，性能优越，（1）触点电流为10安，可满足一般需要，（2）在照明线路中，使用步仅继电器和自复式按钮开关，可实现多点控制，做到布线简单，节约线材，还可以做到不必改动线路就可任意扩展或改变按钮开关位置，灵活方便。（3）用电子开关电路和遥控器控制按钮开关，可实现多点无线控制。由于步进继电器具有以上特点，目前已被广泛的应用到各个领域中。
时间继电器类型及特点
时间继电器类型及特点 1、空气阻尼式时间继电器又称为气囊式时间继电器,它是根据空气压缩产生的阻力来进行延时的,其结构简单,价格便宜,延时范围大(0.4~180s ,但延时精确度低。 2、电磁式时间继电器延时时间短(0.3~1.6s ,但它结构比较简单,通常用在断电延时场合和直流电路中。 3、电动式时间继电器的原理与钟表类似,它是由内部电动机带动减速齿轮转动而获得延时的。这种继电器延时精度高,延时范围宽(0.4~72h ,但结构比较复杂,价格很贵。 4、晶体管式时间继电器又称为电子式时间继电器,它是利用延时电路来进行延时的。这种继电器精度高,体积小。 时间继电器可分为通电延时型和断电延时型两种类型。 以空气阻尼式时间继电器为例来说明时间继电器的工作原理 空气阻尼型时间继电器的延时范围大 (有 0.4~60s 和 0.4~180s 两种 , 它结构简单 , 但准确度较低。 当线圈通电时, 衔铁及托板被铁心吸引而瞬时下移, 使瞬时动作触点接通或断开。但是活塞杆和杠杆不能同时跟着衔铁一起下落, 因为活塞杆的上端连着气室中的橡皮膜, 当活塞杆在释放弹簧的作用下开始向下运动时,橡皮膜随之向下凹 , 上面空气室的空气变得稀薄而使活塞杆受到阻尼作用而缓慢下降。经过一定时间, 活塞杆下降到一定位置, 便通过杠杆推动延时触点动作,使动断触点断开, 动合触点闭合。从线圈通电到延时触点完成动作, 这段时间就是继电器的延时时间。延时时间的长短可以用螺钉调节空气室进气孔的大小来改变。吸引线圈断电后,继电器依靠恢复弹簧的作用而复原。空气经出气孔被迅速排出。时间继电器:当加上或除去输入信号时, 输出部分需延时或限时到规定的时间才闭合或断开其被控线路的继电器。
热继电器的结构及工作原理图解
热继电器的结构及工作原理图解
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热继电器的结构及工作原理图解 热继电器是用于电动机或其它电气设备、电气线路的过载保护的保护电器。 电动机在实际运行中，如拖动生产机械进行工作过程中，若机械出现不正常的情况或电路异常使电动机遇到过载，则电动机转速下降、绕组中的电流将增大，使电动机的绕组温度升高。若过载电流不大且过载的时间较短，电动机绕组不超过允许温升，这种过载是允许的。但若过载时间长，过载电流大，电动机绕组的温升就会超过允许值，使电动机绕组老化，缩短电动机的使用寿命，严重时甚至会使电动机绕组烧毁。所以，这种过载是电动机不能承受的。热继电器就是利用电流的热效应原理，在出现电动机不能承受的过载时切断电动机电路，为电动机提供过载保护的保护电器。 热继电器工作原理示意图如图1
图1 热继电器工作原理示意图 1——热元件，2——双金属片，3——导板，4——触点 热继电器的结构如图2所示。 图中：1——电流调节凸轮，2——片簧（2a，2b），3——手动复位按钮，4——弓簧片，5——主金属片，6——外导板，7——内导板，8——常闭静触点，9——动触点，10——杠杆，11——常开静触点（复位调节螺钉），12——补偿双金属片，13——推杆，14——连杆，15——压簧 使用热继电器对电动机进行过载保护时，将热元件与电动机的定子绕组串联，将热继电器的常闭触头串联在交流接触器的电磁线圈的控制
电路中，并调节整定电流调节旋钮，使人字形拨杆与推杆相距一适当距离。当电动机正常工作时，通过热元件的电流即为电动机的额定电流，热元件发热，双金属片受热后弯曲，使推杆刚好与人字形拨杆接触，而又不能推动人字形拨杆。常闭触头处于闭合状态，交流接触器保持吸合，电动机正常运行。 若电动机出现过载情况，绕组中电流增大，通过热继电器元件中的电流增大使双金属片温度升得更高，弯曲程度加大，推动人字形拨杆，人字形拨杆推动常闭触头，使触头断开而断开交流接触器线圈电路，使接触器释放、切断电动机的电源，电动机停车而得到保护。 热继电器其它部分的作用如下：人字形拨杆的左臂也用双金属片制成，当环境温度发生变化时，主电路中的双金属片会产生一定的变形弯曲，这时人字形拨杆的左臂也会发生同方向的变形弯曲，从而使人字形拨杆与推杆之间的距离基本保持不变，保证热继电器动作的准确性。这种作用称温度补偿作用。 螺钉8是常闭触头复位方式调节螺钉。当螺钉位置靠左时，电动机过载后，常闭触头断开，电动机停车后，热继电器双金属片冷却复位。常闭触头的动触头在弹簧的作用下会自动复位。此时热继电器为自动复位状态。将螺钉逆时针旋转向右调到一定位置时，若这时电动机过载，热继电器的常闭触头断开。其动触头将摆到右侧一新的平衡位置。电动机断电停车后，动触头不能复位。必须按动复位按钮后动触头方能复位。此时热继电器为手动复位状态。若电动机过载是故障性的，为了避免再次轻易地起动电动机，热继电器宜采用手动复位方式。若
热继电器的结构及工作原理61706
热继电器的结构及工作原理 热继电器是用于电动机或其它电气设备、电气线路的过载保护的保护电器。电动机在实际运行中，如拖动生产机械进行工作过程中，若机械出现不正常的情况或电路异常使电动机遇到过载，则电动机转速下降、绕组中的电流将增大，使电动机的绕组温度升高。若过载电流不大且过载的时间较短，电动机绕组不超过允许温升，这种过载是允许的。但若过载时间长，过载电流大，电动机绕组的温升就会超过允许值，使电动机绕组老化，缩短电动机的使用寿命，严重时甚至会使电动机绕组烧毁。所以，这种过载是电动机不能承受的。热继电器就是利用电流的热效应原理，在出现电动机不能承受的过载时切断电动机电路，为电动机提供过载保护的保护电器。 热继电器工作原理示意图如图1 图1 热继电器工作原理示意图 1——热元件，2——双金属片，3——导板，4——触点 热继电器的结构如图2所示。 图1 热继电器结构示意图 图中：1——电流调节凸轮，2——片簧（2a，2b），3——手动复位按钮，4——弓簧片，5——主金属片，6——外导板，7——内导板，8——常闭静触点，9——动触点，10——杠杆，11——常开静触点（复位调节螺钉），12——补偿双金属片，13——推杆，14——连杆，15——压簧
使用热继电器对电动机进行过载保护时，将热元件与电动机的定子绕组串联，将热继电器的常闭触头串联在交流接触器的电磁线圈的控制电路中，并调节整定电流调节旋钮，使人字形拨杆与推杆相距一适当距离。当电动机正常工作时，通过热元件的电流即为电动机的额定电流，热元件发热，双金属片受热后弯曲，使推杆刚好与人字形拨杆接触，而又不能推动人字形拨杆。常闭触头处于闭合状态，交流接触器保持吸合，电动机正常运行。 若电动机出现过载情况，绕组中电流增大，通过热继电器元件中的电流增大使双金属片温度升得更高，弯曲程度加大，推动人字形拨杆，人字形拨杆推动常闭触头，使触头断开而断开交流接触器线圈电路，使接触器释放、切断电动机的电源，电动机停车而得到保护。 热继电器其它部分的作用如下：人字形拨杆的左臂也用双金属片制成，当环境温度发生变化时，主电路中的双金属片会产生一定的变形弯曲，这时人字形拨杆的左臂也会发生同方向的变形弯曲，从而使人字形拨杆与推杆之间的距离基本保持不变，保证热继电器动作的准确性。这种作用称温度补偿作用。 螺钉8是常闭触头复位方式调节螺钉。当螺钉位置靠左时，电动机过载后，常闭触头断开，电动机停车后，热继电器双金属片冷却复位。常闭触头的动触头在弹簧的作用下会自动复位。此时热继电器为自动复位状态。将螺钉逆时针旋转向右调到一定位置时，若这时电动机过载，热继电器的常闭触头断开。其动触头将摆到右侧一新的平衡位置。电动机断电停车后，动触头不能复位。必须按动复位按钮后动触头方能复位。此时热继电器为手动复位状态。若电动机过载是故障性的，为了避免再次轻易地起动电动机，热继电器宜采用手动复位方式。若要将热继电器由手动复位方式调至自动复位方式，只需将复位调节螺钉顺时针旋进至适当位置即可。 有些型号的热继电器还具有断相保护功能。其结构示意图如图3所示： 图3 差动式断相保护装置示意图 （a）通电前，（b）三相通有额定电流，（c）三相均衡过载，（d）一相断电故障 热继电器的断相保护功能是由内、外推杆组成的差动放大机构提供的。当电动机正常工作时，通过热继电器热元件的电流正常，内外两推杆均向前移至适当位置。当出现电源一相断线而造成缺相时，该相电流为零，该相的双金属片冷却复位，使内推杆向右移动，另两相的双金属片因电流增大而弯曲程度增大，使外推杆更向左移动，由于差动放大作用，在出现断相故障后很短的时间内就推动常闭触头使其断开，使交流接触器释放，电动机断电停车而得到保护。
继电器常用种类及说明
1、过电流继电器 过电流继电器，简称CO，是从电流超过其设定值而动作的继电器，可做系统线路及过载的保护用，最常用的是感应型过电流继电器，是利用电磁铁与铝或铜制的旋转盘相对，依靠电磁感应原理使旋转圆盘转动，以达到保护作用。 动作原理： 感应型过电流继电器是利用电流互感器二次侧电流，在继电器内产生磁场，以促使圆盘转动，但流过的电流必须大于电流标置板的电流值才能转动。 2、过电压继电器 过电压继电器，简称OV，它的主要用途在于当系统的异常电压上升至120%额定值以上时，过电压继电器动作而使断路器跳脱保护电力设备免遭损坏，感应式过电压继电器的构造及动作原理和过电流继电器相似，只有主线圈不同。 3、欠电压继电器 欠电压继电器，简称UV，其构造与过电压继电器相同，所不同的是内部触头及当外加电压时转盘会立即转动。 110V额定电压220V额定电压 电压标置范围60~80V 电压标置范围120~160V （60、65、70、75、80V）（120、130、140、150、160V） 4、接地过电压继电器 接地过电压继电器，简称OVG，或称接地报警继电器简称GR，其构造与过电压继电器相同，使用与三相三线非接地系统，接于开口三角形接地的接地互感器上，用以检知零相电压。 4、接地过电流继电器 接地过电流继电器，简称GCR，是一种高压线路接地保护继电器。 主要用途： （1）高电阻接地系统的接地过电流保护；（2）发电机定子绕组的接地保护； （3）分相发电机的层间短路保护；（4）接地变压器的过热保护。 5、选择性接地继电器 选择性接地继电器，简称SG，又称方向性接地继电器，简称DG，使用于非接地系统作配电线路保护作用，架空线及电缆系统也能使用。 选择性接地继电器：由接地电压互感器检出零相序电流如遇线路接地时，选择性接地继电器能确实地表示故障线路而发生警报，并按照其需要选择故障线路将其断开，而继续向正常线路送电。 6、缺相继电器 缺相继电器，简称OPR，或缺相保护继电器，简称PHR，在三相线路中，当电源端有一线断路而造成单相时，若未有立即将线路切断，将使电动机单相运转而烧毁。 7、比率差动继电器 比率差动继电器，简称RDR，被应用做变压器交流电动机，交流发电机的差
时间继电器的分类结构及选用原则
时间继电器的分类、结构及选用原则时间继电器是一种利用电磁原理或机械动作原理实现触点延时接通或断开的自动控制电器，其种类很多，常用的有电磁式、空气阻尼式、电动式和晶体管式等。 时间继电器图形符号及文字符号如图1所示。 图1 时间继电器图形符号及文字符号 1．直流电磁式时间继电器 在直流电磁式电压继电器的铁心上增加一个阻尼铜套，即可构成时间继电器，其结构示意图如图2所示。它是利用电磁阻尼原理产生延时的，由电
磁感应定律可知，在继电器线圈通断电过程中铜套内将感应电势，并流过感应电流，此电流产生的磁通总是反对原磁通变化。 图2 带有阻尼铜套的铁心示意图 1-铁心 2-阻尼铜套 3-绝缘层 4-线圈 电器通电时，由于衔铁处于释放位置，气隙大，磁阻大，磁通小，铜套阻尼作用相对也小，因此衔铁吸合时延时不显著(一般忽略不计)。 而当继电器断电时，磁通变化量大，铜套阻尼作用也大，使衔铁延时释放而起到延时作用。因此，这种继电器仅用作断电延时。 这种时间继电器延时较短，JT3系列最长不超过5s，而且准确度较低，一般只用于要求不高的场合。 2．空气式时间继电器
空气阻尼式时间继电器，是利用空气阻尼原理获得延时的。它由电磁系统、延时机构和触点三部分组成，电磁机构为直动式双E型，触点系统是借用LX5型微动开关，延时机构采用气囊式阻尼器。 空气阻尼式时间继电器，既具有由空气室中的气动机构带动的延时触点，也具有由电磁机构直接带动的瞬动触点，可以做成通电延时型，也可做成断电延时型。电磁机构可以是直流的，也可以是交流的。 3．半导体时间继电器 电子式时间继电器在时间继电器中已成为主流产品，电子式时间继电器是采用晶体管或集成电路和电子元件等构成．目前已有采用单片机控制的时间继电器。电子式时间继电器具有延时范围广、精度高、体积小、耐冲击和耐振动、调节方便及寿命长等优点，所以发展很快，应用广泛。 半导体时间继电器的输出形式有两种：有触点式和无触点式，前者是用晶体管驱动小型磁式继电器，后者是采用晶体管或晶闸管输出。 4．单片机控制时间继电器
两种气体继电器的结构原理 柴大为
两种气体继电器的结构原理柴大为 发表时间：2018-03-12T15:31:46.660Z 来源：《电力设备》2017年第29期作者：柴大为 [导读] 摘要：气体继电器（也称为瓦斯继电器）是保护油浸式变压器的一种装置，安装在变压器储油柜与本体之间的油管上，当油浸式变压器的内部发生故障时，由于电弧将使绝缘材料分解并产生大量的气体，其产气速率与产气量与故障严重程度有关。 （国网内蒙古东部电力有限公司检修分公司兴安运维分部 137400） 摘要：气体继电器（也称为瓦斯继电器）是保护油浸式变压器的一种装置，安装在变压器储油柜与本体之间的油管上，当油浸式变压器的内部发生故障时，由于电弧将使绝缘材料分解并产生大量的气体，其产气速率与产气量与故障严重程度有关。当变压器内部故障而使油分解产生气体或造成油流涌动时，气体继电器的相应接点动作，接通指定的二次回路，并及时发出信号告警（轻瓦斯）或启动主变各侧断路器跳闸（重瓦斯）。 本文中主要介绍了油浸式变压器常用的两种气体继电器，对不同气体继电器的结构原理及应用范围进行阐述。 关键词：气体继电器；结构；原理；应用范围 1引言 变压器发生内部故障时，由于故障电流和故障点处电弧的作用，使变压器内部绝缘油因受热而分解产生气体，气体将从变压器本体油箱内流向储油柜上部，故障严重时将迅速产生大量气体且绝缘油体积迅速膨胀，此时会有强烈的绝缘油流和气流迅速冲向储油柜上部，利用变压器本体内部故障时的这一特点构成的保护称之为瓦斯保护。 变压器瓦斯保护中最为重要的元件为变压器气体继电器，将气体继电器安装在变压器本体与储油柜之间的导油管上，以便监测变压器内部故障产生的气体及油流，从而迅速做出判断避免变压器发生进一步损坏。目前，现场中常用的气体继电器有两种结构，一种为单浮球气体继电器，另一种为双浮球气体继电器。 2两种瓦斯继电器的结构原理 2.1单浮球气体继电器结构 如图1所示为一种常用的单浮球气体继电器内部结构，各部位结构说明如下： 1-探针，2-放气阀，3-重锤，4-开口杯，5-永久磁铁，6-干簧触点（轻瓦斯），7-磁铁，8-挡板，9-接线端子，10-流速整定螺杆，11-干簧触点（重瓦斯），12-终止档，13-弹簧。 变压器本体内部发生轻微故障时，绝缘油受热分解出的气体沿本体与储油柜之间的导油管运动至气体继电器处，聚集在顶盖处形成一定的压力，逐渐将变压器油面高度压低，开口杯所受浮力减小，随油面的降低开始转动，使磁铁5与干簧触点6接触，从而吸引干簧触点接通，发出轻瓦斯信号。同理，当变压器本体漏油时，随着气体继电器内部油面降低，气体继电器动作情况相同，发出轻瓦斯信号。 双浮子气体继电器轻瓦斯与重瓦斯动作原理与单浮子继电器相同，但是由于增加了下浮子，使得继电器在变压器绝缘油严重泄露时也可以向变压器各侧开关发出跳闸信号，对变压器的保护更加全面。 3两种气体继电器的应用 3.1单浮球气体继电器应用 单浮球气体继电器普遍应用于各类油浸式变压器及有载分接开关上，当变压器内部发生轻微故障，气体逐渐积累至气体继电器内部，可使继电器发出轻瓦斯信号。由于气体继电器内挡板动作方向朝向储油柜方向，所以只有在变压器内部发生严重故障时，气体继电器才能够发出跳闸命令同时发出重瓦斯信号。 如果由于某种原因导致变压器油大量泄漏，本体内油位迅速下降，由于此时油流方向从储油柜流向本体，不会冲击气体继电器挡板动作，即使油位已经下降至露出变压器铁芯，开关短时内仍不会跳闸，将导致变压器损坏。 目前，现场使用的容量在120MVA及以下的主变压器密封较好，运行期间基本不存在变压器油大量泄漏的风险，因此单浮球气体继电器得到了广泛的应用。 3.2双浮球气体继电器的应用 随着用电需求的增加和电网发展的要求，越来越多的大容量变压器逐步投入运行，同时对变压器本体的消防装置要求也不断提高，现场一般要求120MVA以上容量的变压器需安装排油充氮灭火装置，避免变压器发生严重故障时引起火灾并进一步扩大。 由于排油充氮灭火装置的安装，在变压器本体上安装了排油电磁阀及充氮电磁阀，大大增加了变压器运行期间绝缘油泄露的风险，因此国家电网十八项反事故措施要求采用排油充氮灭火装置的主变，需安装双浮球气体继电器，避免由于排油充氮装置的故障导致电磁阀失效引起绝缘油大量泄露造成变压器烧损。 4结语 目前，双浮球气体继电器广泛应用于大容量变压器上，在实现传统气体继电器功能的同时，也能够对绝缘油异常泄露进行保护，对变压器的保护更全面，大大提高了设备运行稳定性。