JPH06284556A - Grounding current detection method for three-phase four-wire circuit - Google Patents

Abstract

PURPOSE:To detect a grounding current of a three-phase four-wire circuit independently of a zero-phase current due to an unbalanced load. CONSTITUTION:Current transformers CT1 to CT4 are provided respectively for four wires of a three-phase four-wire circuit; all current transformers are connected together in parallel thereby creating four current transformer residual circuit 2; and a grounding current protection relay 51G is connected to this residual circuit. A zero-phase current due to an unbalanced load L1 of the three- phase four-wire circuit flows to a current transformer CT4 at the neutral line but not to the residual circuit 2. When a grounding accident F occurs, the grounding current flows to the grounding phase, so that a zero-phase current due to the grounding current IG flows to the residual circuit 2. Thus, the grounding current protection relay is operated only by the zero-phase current by the grounding current without being affected by the zero-phase current due to the unbalanced load L1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low resistance grounding type three-phase four
The present invention relates to a ground fault current detection method in a wire circuit.

[0002]

2. Description of the Related Art Conventionally, in the ground fault detection of a three-phase circuit, a current transformer is provided for each phase to detect a zero-phase current, and this current is passed through a ground fault current protection relay for detection. When the current transformer is 300 / 5A or less, as shown in FIG. 3, the current transformer CT ₁ . Each of the secondary windings a of CT ₂ and CT ₂ is connected in parallel, and a ground fault current protection relay 51G is connected in the residual circuit 2 in which both ends of the parallel circuit 1 are connected.

When the current transformer is 300/5 A or more, as shown in FIG. 4, the current transformer CT ₁ . CT ₂ , C
Parallel circuit 1 in which each secondary winding a is connected in parallel using T _2.
Both ends of each are short-circuited, and each tertiary winding b is used as a delta connection circuit 3, and a ground fault current protection relay 51G is connected in series in the circuit.

[0004]

In the three-phase four-wire type distribution system, the single-phase load L ₁ is connected as shown in FIGS. The zero-phase current I _N flows.

Therefore, in the case of the circuit of FIG. 3 described above, when the ground fault F occurs, the current Ir of the residual circuit 2 includes the zero-phase current In flowing in the neutral line current I _N , so that the ground fault current protection relay. The 51G malfunctions due to this zero-phase current I _N.

In the case of the circuit of FIG. 4, the ground fault F
There to occur, the current Ior delta circuit 3 because it contains zero-phase current In fraction flowing through the neutral current I _N, the ground fault current protective relay 51G to malfunction.

Therefore, in any case, it is necessary to set the ground fault current protection relay 51G in consideration of the zero-phase current I _{N due} to the unbalanced load flowing through the neutral line N, and to set the ground fault current protection relay 51G. Is set to be less accurate.

The present invention has been made in view of the above problems of the prior art, and its object is to make the ground fault current of a three-phase four-wire circuit independent of the zero-phase current due to an unbalanced load. It is an object of the present invention to provide a ground fault current detection method for a three-phase four-wire circuit that can detect the current.

[0009]

In order to achieve the above object, a ground fault current system of a three-phase four-wire circuit according to the present invention is
A current transformer is provided on each of the four wires of the three-phase four-wire circuit, and each of the two
The following windings are connected in parallel to form a four-current transformer residual circuit, and a ground fault current protection relay is connected to this residual circuit.

When a current transformer with a tertiary winding is used, a current transformer with a tertiary winding is provided for each phase wire of the three-phase four-wire circuit and the current transformer is a neutral wire. Or, install a current transformer with a tertiary winding in which the tertiary winding is open, connect the secondary winding of each current transformer in parallel, and configure the tertiary winding of each phase current transformer in a delta circuit. It is configured by connecting a ground fault current protection relay in series with this delta circuit.

[0011]

[Function] Since the neutral line side current transformer forms a closed circuit with each phase converter, the zero-phase current due to the unbalanced load flows to the neutral line side current transformer and does not flow to the residual circuit of the current transformer 4. . When a ground fault occurs, the ground fault current flows in the ground fault phase, and therefore flows as a zero-phase current in the residual circuit of the four current transformer. Therefore, the ground fault current protection relay connected to the residual circuit of the four current transformer operates only by the zero phase current due to the fault current regardless of the unbalanced load.

When a current transformer with a tertiary winding is used, the neutral line side current transformer forms a closed circuit with each phase current transformer.
The zero-phase current due to the unbalanced load does not flow in the delta circuit because it flows in the neutral line side current transformer. When a ground fault accident occurs, the ground fault current flows in the ground fault phase, and thus flows as a zero-phase current in the delta circuit. Therefore, the ground fault current protection relay connected in series with the delta circuit operates only by the zero phase current due to the fault current regardless of the unbalanced load.

[0013]

Embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 Referring to FIG. 1, CT _{1 to} CT ₃ are current transformers provided in the respective phases R, T and S, CT ₄ is a current transformer provided in the neutral line N, and 51G is a current transformer CT. A ground fault current protection relay connected to a 4CT residual circuit 2 in which both ends of a parallel circuit 1 in which _{1 to} CT ₄ are connected in parallel are connected, L ₁ indicates a single-phase load (unbalanced load).

Next, the operation of this circuit will be described. If there is no ground fault current I _G , the current transformer CT ₄ attached to the neutral line N
Forms a closed circuit with each of the phase current transformers CT _{1 to} CT ₃ , so that the zero-phase current I _N flowing by the unbalanced load L ₁ is the neutral line side current transformer CT.
_Since it flows into ₄ , the current In component does not flow in the residual circuit 2 connecting the ground fault current protection relay 51G.

When a ground fault F occurs in the R phase in this state, the ground fault current I _G flows only in the R phase, so that the zero-phase current due to the ground fault current I _G flows in the residual circuit 2 as a secondary current transformer. The flow ground fault current protection relay 51G is operated as the ground fault current Ig.

As described above, no current normally flows in the residual circuit 2 and a current flows only when a ground fault occurs, so that the ground fault current relay can be set accurately and the ground fault can be set accurately. Can be protected.

Embodiment 2 Referring to FIG. 2, CT _{1 to} CT ₃ are current transformers with tertiary windings provided in the respective phases R, T and S, and CT ₄ are current transformers or 3 provided in the neutral line N. A parallel circuit 1 in which the secondary winding a of the current transformers CT _{1 to} CT ₄ is connected in parallel in a current transformer with a tertiary winding in which the secondary winding is open.
The residual circuit is not made as it is.

[0019] 51G is 3 winding b of the current transformer CT ₁ ~CT ₃
, A ground fault current protection relay connected in series in a delta connected circuit, L ₁ represents a single phase load.

Next, the operation of this circuit will be described. If there is no ground fault current I _G , the current transformer CT ₄ attached to the neutral line N
Of the secondary winding a of each of the phase current transformers CT _{1 to} CT ₃
In order to form a closed circuit with, the zero-phase current In flowing by the unbalanced load L ₁ flows into the neutral wire N-side current transformer CT ₄ and the third winding b-side delta circuit 3 connecting the ground fault current protection relay is connected. Does not flow to.

When a ground fault F occurs in the R phase in this state, the ground fault current I _G flows only in the R phase, so that the current transformer 3 outputs a zero-phase current due to the ground fault current I _G to the delta circuit 3.
The next ground fault current Ig flows to operate the ground fault protection relay 51G.

Therefore, the ground-fault current protection relay can be used with an accurate setting as in the first embodiment.

[0023]

Since the present invention is configured as described above, it has the following effects.

(1) Only the zero-phase current due to the fault current flows through the ground fault current protection relay, and the zero-phase current due to the unbalanced load current due to the single-phase load does not flow. The accuracy of the fault protection is improved.

(2) Since the accuracy of ground fault detection is improved, the reliability of the three-phase four-wire power distribution system is improved.

(3) Since the accuracy of the ground fault detection is improved, the damage to the electric equipment caused by the ground fault is reduced and the safety is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment.

FIG. 3 is a circuit diagram showing a first conventional example.

FIG. 4 is a circuit diagram showing a second conventional example.

[Explanation of symbols]

CT ₁ to CT ₄ ... current transformer a ... current transformer secondary winding b ... transformer tertiary winding L ₁ ... single-phase load (unbalanced load) 1 ... parallel circuit 2 ... residual circuit 3 ... Delta circuit

Claims (2)

[Claims] 1. A current transformer is provided on each of the four wires of a three-phase four-wire circuit, and each secondary winding thereof is connected in parallel to form a four-current transformer residual circuit. Connect the protective relay,
A ground fault current detection method for a three-phase four-wire circuit, characterized in that the zero-phase current due to an unbalanced load does not flow in the residual circuit. 2. A three-phase four-wire circuit with each phase wire provided with a current transformer with a tertiary winding, and a neutral wire with a current transformer or a tertiary winding with the tertiary winding open. A current transformer is provided, the secondary windings of each current transformer are connected in parallel, and the tertiary winding of each phase current transformer is connected to a delta circuit, and a ground fault current is connected in series in this delta circuit. A ground fault current detection method for a three-phase, four-wire circuit characterized by connecting a protective relay so that zero-phase current due to unbalanced load does not flow in the delta circuit.