JPH0667100B2 - Undervoltage relay with current compensation - Google Patents

Description

Detailed Description of the Invention A. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an undervoltage relay device with current compensation.

B. SUMMARY OF THE INVENTION The present invention is a foot voltage relay with current compensation for use in a 22KV system or a 6.6KV system, in which a current transformer is provided in a three-phase system, for example, two phases, R-phase and T-phase. By inputting the output current _R and the interphase voltage _RS , the output current _T and the interphase voltage _ST, and both output currents _R and _T and the interphase voltage _TR into the respective operation units and performing the operation processing, the By using this, a relay device having the function of an undervoltage relay with current compensation for three phases is obtained.

C. Conventional technology Conventionally, an undervoltage relay with current compensation (hereinafter referred to as an undervoltage relay) has been used for protection of a long-distance ultra-high voltage system, but for protection of a 22KV system or a 6.6KV system, It has never been applied for such a reason.

(a) The operation principle is complicated, and (b) the distribution system is relatively short and constant. However, with the spread of microcomputers in recent years, relay characteristics are realized by digital operation (program). As a result, the constraint in item (a) above has become less of an issue. However, when applying an undervoltage relay to a 22KV system or a 6.6KV system, a current transformer (C
There is a problem with the installation of T). This is 22KV system or 6.6KV
In the system, since the information was obtained from the system by installing only two phases of CT, the 3CT established in the above ultra-high voltage system
The protection method of the undervoltage relay by the method cannot be immediately applied as it is. FIG. 5 is a configuration diagram of an undervoltage relay based on the 3CT system. In the figure, 1, 2 and 3 are undervoltage relays,
4, 5 and 6 is the main CT, R, S, T is the _{phase, V R, V S, V} T is low system voltage of from the instrument transformers or the like.

Here, the operation formulas of the undervoltage relays 1, 2 and 3 of the ultra-high voltage system by the 3CT system are as follows.

｜ _RS − _RS・ K ₀ ｜ ≦ K ₁ (RS phase relay)… (1) ｜ _ST − _ST・ K ₀ ｜ ≦ K ₁ (ST phase relay)… (2) ｜ _TR − _TR・ K ₀ ｜ ≦ K ₁ (TR phase relay) (3) However, _RS , _ST , _TR are line voltage, _RS , _ST , _TR
Is the line current and K ₀ and K ₁ are set values.

D. Problems to be Solved by the Invention Since (1) to (3) above are the operation formulas of the undervoltage relay established by the 3CT system, when applying the above formulas (1) to (3) to the 2CT system, _RS There is a problem that the current of _ST and _ST cannot be taken in and the operation formula is not established.

E. As shown in FIG. 1, the present invention provides current transformers in a three-phase system, for example, two phases of R phase and T phase, and outputs currents of these current transformers.
_R , _T and each phase voltage V _R , V _S , V _T from the instrument transformer are processed by the relay operation unit of the following equation.

_{| RS -K 0 · 2 R |} ≦ K 1 ...... (4) | ST + K 0 · 2 T | ≦ K 1 ...... (5) | TR -K 0 · (TR) | ≦ K 1 ...... (6) However, _{RS, ST, TR} is the line voltage, _{R, S, T} is the phase current, K _0, K ₁ is the setting value.

F. Operation When the settling value K ₁ is smaller than or equal to the above equation, the relay operation unit always performs a positive operation regardless of whether a two-phase short circuit or a three-phase short circuit. As a result, even if the undervoltage relay based on 2CT is applied to the three-phase system, it is possible to surely protect against an accident.

G. Example In FIG. 1, R, S and T are phases of a three-phase system, and CB
_R, CB _S, CB _T Hashiyadan unit is V _R, V _S, V _T is low bus voltage that is connected to, for example, a potential transformer PD. Reference numerals 10 and 11 denote current transformers arranged in the R and T phases, and the output current I _R detected by the current transformer 10 is input to an undervoltage relay 7 whose details are shown in FIG. In addition, the output current I _R detected by the current transformer 11
Is input to the undervoltage relay 8. Further current transformers 10, 11
Output current I _R detected by, I _T is input to the undervoltage relay 9.

The line voltage V _RS is applied to the undervoltage relay 7, the line voltage V _ST is applied to the undervoltage relay 8, and the line voltage V _TR is applied to the undervoltage relay 9.

The undervoltage relay 7 is the first relay computing unit RY shown in FIG. 2A.
It is composed of P ₁ , and the first relay operation unit RYP ₁ is | _RS −
The output 27-1 is transmitted when the value K ₀ · 2 _S | ≦ K ₁ is calculated and is less than or equal to the set value K ₁ . Similarly, the undervoltage relay 8 is composed of the second relay operation unit RYP ₂ shown in FIG. 2B, performs the operation of | _ST + K ₀ · 2 _T | ≦ K ₁ and outputs 27
-2 is transmitted. Further, the undervoltage relay 9 is composed of a third relay computing unit RYP ₃ shown in FIG. 2C, and | _TR- K ₀ ·
( _T − _R ) | ≦ K ₁ is calculated and output 27-3 is sent.

The arithmetic expressions of the first to third relay arithmetic units RYP _{1 to} RYP ₃ were derived as follows. Then, in the case of 2CT, the phase current I _S is zero.

(a) Indicates the line current when three conventional current transformers are used and the line current when two current transformers are used when two phases, R and S, are short-circuited. And becomes the following formula. _RS (in case of 3CT) = _R - _S = 2 _R ...... (7) _RS (in case of 2CT) = _R - _S = _R ...... (8) (b) When two phases of S phase and T phase are short-circuited Is the same as above 3
The case of CT and 2CT is as follows. _ST (3CT) = _S - _T = 2 _S = -2 _T (9) _ST (2CT) = _S - _T = _-T (10) (c) T-phase and R-phase are short-circuited. When the same as above 3
The case of CT and 2CT is as follows. _TR (3CT) = _T - _R = -2 _T ...... (11) _TR (2CT) = _T - _R = 2 _T ...... (12) (d) In case of three-phase short circuit, 3CT and 2CT The following equation shows the case. _{TR (3CT) = TR ...... (} 13) TR (2CT) = TR ...... (14) then the event of a short circuit due to insufficient voltage relay according 2CT (provided the CT to R-phase and T-phase) ( FIG. 3 shows the voltage and current vectors of the short circuit pattern) and the voltage and current vectors of the relay calculator. In FIG. 3, the vector indicated by the broken line is the relay input in the case of 3CT. As is apparent from FIG. 3, the first to third relay arithmetic units RYP ₁
~ RYP ₃ always operates correctly regardless of the short circuit pattern of three-phase short circuit or three-phase short circuit. As a result, even if an undervoltage relay based on 2CT is applied to a 22KV system or a 6.6KV system, it is possible to reliably protect against an accident.

FIG. 4 is a block diagram showing another embodiment of the present invention. FIG. 4 shows the outputs of the overcurrent relay 51 and the undervoltage relay 27 according to the present invention input to the OR circuit OR, and the CB can be tripped by either relay output. is there. Usually 22KV or
In the 6.6KV system feeder, the 2CT method was adopted, and short-circuit protection was performed only by the overcurrent relay. However, if the feeder has a long constant length and a large capacity demand is connected as a load, there will be no difference between the load current at the normal time and the current at the time of failure at the end of the feeder. Therefore, the overcurrent relay cannot provide sufficient protection, and the protection range is limited. However, by configuring as shown in FIG. 4, it is possible to surely protect even in the above case.

E. EFFECTS OF THE INVENTION As described above, according to the present invention, even two current transformers can be applied to an undervoltage relay with current compensation for three phases, so that the current is transformed into a 22KV system or a 6.6KV system. The system can be protected without adding additional equipment. Further, regarding the current intake, the same effect can be obtained by doubling the current in the R-phase and ST-phase relays by using an auxiliary current transformer or the like, or by doubling the settling value K ₀ in the TR-phase relay.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2A,
B and C are diagrams for explaining the main part of the present invention, FIG. 3 is a vector diagram of a relay according to the present invention, FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a conventional example. It is a connection diagram showing. 7, 8, 9 ... Undervoltage relay with current compensation, 10, 11 ... Current transformer, RYP _{1 to} RYP ₃ ... 1st to 3rd relay arithmetic unit.

Claims (1)

[Claims] 1. A current transformer is provided in two phases, R phase and T phase, out of the three-phase system R, S, T phase, and the output current I _R of each current transformer,
R, S, T phase voltages V _R , V _S from I _T and the instrument transformer,
V _T is calculated by the first to third relay calculation units of the following equation, and | V _RS −K ₀ · 2I _R | ≦ K ₁ | V _ST −K ₀ · 2I _T | ≦ K ₁ | V _TR − _{K 0 · (I T -I R} ) | ≦ K 1 _{where, V RS, V ST, V} TR is the line _{voltage, I R, I S, I} T is the phase current, K _0, K ₁ in the setpoint An undervoltage relay device with current compensation, wherein it is determined that a two-phase short circuit or a three-phase short circuit has occurred when the set value is smaller than or equal to K ₁ .