JPH0145295B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transformer protection device, and particularly to a ground fault protection device for a three-phase transformer circuit used in power plants (thermal power, hydropower, nuclear power).

Conventionally, there has been a device of this type as shown in FIG. 1 is a protected transformer; 2 is a grounding resistor installed to suppress ground fault current; 3 is a current transformer for detecting ground fault current; and 4 is a ground fault relay operated by ground fault current. be.

Next, the operation will be explained. When a ground fault occurs on the star (〓) side of the transformer 1, a closed circuit is formed between the fault point and the neutral point grounding point, and the ground fault current Ig flows through the earthing resistor 2, and the current transformer The ground fault relay 4 works to detect the current induced on the secondary side of the ground fault relay 3.

The conventional ground fault protection device for a transformer has the disadvantage that when the ground resistor 2 has a high resistance, the ground fault current becomes small and the detection sensitivity becomes low.

Furthermore, according to this method, a ground fault on the delta (△) side of the transformer can be detected by the ground fault relay 4.
There were drawbacks such as the inability to detect and the need to add other protection methods.

This invention was made in order to eliminate the drawbacks of the above-mentioned conventional devices, and aims to improve the sensitivity and expand the protection range by combining the conventional ground fault protection device with a ratio differential relay. There is.

The configuration of the present invention to achieve such an object includes a ratio differential relay that detects zero-sequence current from each line on the primary side and secondary side of a three-phase transformer using an operating coil and a suppression coil, and the above-mentioned 3. phase transformer 1
a neutral point current detection circuit for detecting a neutral point current by a coil from a neutral point on the next side, the operating coil and a part of the coil are magnetically and harmonically coupled;
The suppression coil and another part of the coil are magnetically differentially coupled, and the zero-sequence current detection circuit on the secondary side of the three-phase transformer of the ratio differential relay and the neutral point current A ground fault protection device for a transformer, characterized in that a detection circuit and a detection circuit are connected in parallel.

The present invention will be explained below with reference to a preferred embodiment of the present invention shown in FIG. 2, the difference from FIG. 1 is that current transformers 5 and 6 are provided on the star side bus bar and delta side bus bar of the transformer 1, respectively, and these current transformers 5 and 6 and current transformer 3 The point is that a ratio differential relay 7 connected to the secondary side is provided. In this case, current transformers 5 and 6 are connected in parallel to each bus bar for the purpose of detecting zero-sequence current.
Further, the ratio differential relay 7 includes an operating coil 8a and suppression coils 9a ₁ and 9a ₂ . Furthermore, the current transformer 3 includes a coil 8b that is magnetically harmonically coupled to the operating coil 8a, and coils 9b ₁ and 9b ₂ that are differentially coupled to the suppression coils 9a ₁ and 9a ₂ , respectively.
and is connected in series to form a neutral point current detection circuit.

Next, the operation will be explained.

For example, when a one-line ground fault occurs on the star side bus of a transformer, the ground fault current Ig flows through a closed circuit including the fault point and the neutral point grounding point. On the secondary side of current transformer 3,
I ₁ induced by the ground fault current Ig flows, and a zero-sequence current also induced by the ground fault current Ig flows on the secondary side of the current transformer 5. Suppression coil 9a ₂ →operation The current flows through a closed circuit consisting of a loop on the secondary side of the coil 8a and the current transformer 5. Note that, as a matter of course, no current is induced on the secondary side of the current transformer 6.

Here, the above-mentioned current I ₁ is applied to the first branch point at the branch point on the secondary side of current transformer 3, which is connected by the line connecting the secondary sides of current transformers 3 and 6 in parallel. (In Fig. 2, the lower side of the secondary side of the current transformer 3) → Suppression coil 9a ₁ → Operating coil 8a → Second
branch point (in Figure 2, above the secondary side of current transformer 3)
→Current Ia flowing through the closed circuit consisting of the loop on the secondary side of current transformer 3; First branch point → Coil 9b ₂ → Coil 9b ₁ → Coil 8b → Second branch point → 2 of current transformer 3 The current is divided equally into the current Ib flowing through the closed circuit consisting of the next loop. Note that the shunted current Ia does not flow to the secondary side of the current transformer 6 because the impedance of the current transformer 6 is large.

Then, currents Ia and Ib having the same magnitude and opposite direction flow in the suppressing coil 9a ₁ and the coil 9b ₁ , so that the torque of the suppressing coil 9a ₁ is canceled out.

Furthermore, the zero-sequence current and the current Ib having opposite directions flow in the suppressing coil 9a ₂ and the coil 9b ₂ , so that the torque of the suppressing coil 9a ₂ becomes small.

On the other hand, in the operating coil 8a and the coil 8b, the direction is the same (zero-sequence current + current Ia) and the current
Ib flows, and the torque of the operating coil 8a is added and becomes larger.

As a result, the current induced on the secondary side of current transformer 3
Even if I ₁ is small, the suppression coils 9a ₁ and 9a ₂
Since the torque of the operating coil 8a becomes smaller and the torque of the operating coil 8a becomes larger, the ratio differential relay 7 operates with good sensitivity.

On the other hand, if a ground fault occurs on the delta side bus of transformer 1, the ground fault current Ig' will be Fault point and grounding resistor (bottom of Figure 2)
flows through a closed circuit formed from A zero-sequence current I ₂ induced by the ground fault current Ig' flows through the secondary side of the current transformer 6. Note that no current is induced on the secondary sides of the current transformers 3 and 5.

Here, the above-mentioned zero-sequence current I ₂ is generated at the branch point on the secondary side of current transformer 6, which is connected by the line connecting the secondary sides of current transformers 3 and 6 in parallel. Branch point (lower side of the secondary side of the current transformer 6 in Fig. 2) → Suppression coil 9a ₁ → Operating coil 8a → Fourth branch point (lower side of the secondary side of the current transformer 6 in Fig. 2) Upper side) → Current Ic flowing through the closed circuit consisting of the secondary loop of current transformer 6
and current Id flowing through a closed circuit consisting of coil 9b ₂ →coil 9b ₁ →coil 8b → secondary loop of current transformer 6. In addition, the shunted current
Ic and Id do not flow to the secondary side of current transformers 5 and 3 because the impedance of current transformers 5 and 3 is large.

Then, currents Ic and Id having the same magnitude and opposite direction flow in the suppression coil 9a ₁ and the coil 9b ₁ , so that the torque of the suppression coil 9a ₁ is canceled out.

On the other hand, currents Ic and Id having the same magnitude and direction flow in the operating coil 8a and the coil 8b, and the torque of the operating coil 8a is added and becomes larger.

As a result, even if the zero-sequence current _I2 induced on the secondary side of the current transformer 6 is small, the torque of the suppression coil _9a1 becomes small and the torque of the operating coil 8a becomes large, so that the ratio differential relay 7 operates with good sensitivity.

In the case of Figure 2, the object of protection changes depending on the installation position of the current transformer, but if the current transformer is installed in the bushing of the transformer body, it becomes a fault detection device inside the transformer, and the current transformer becomes a transformer. If attached to the connection busbars at both ends, it becomes a failure detection device for the inside of the transformer and the transformer connection busbars. In either case, the ground fault protection device of the present invention provides similar effects.

As described above, according to the present invention, even if the ground resistance is large and the ground fault current is small, the relative difference between the built-in operating coil and the suppression coil is The difference in excitation force increases, and highly sensitive ground fault detection can be expected, and the protection range can be expanded.
The advantage is that there is no need to add another relay.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram schematically showing a conventional ground fault protection device for a transformer, and FIG. 2 is a circuit diagram schematically showing a preferred embodiment of the ground fault protection device for a transformer according to the present invention. be. 1...Transformer, 3,5,6...Current transformer, 7...
Ratio differential relay, 8a... Operating coil, 8b, 9
b ₁ , 9b ₂ ... coil, 9a ₁ , 9a ₂ ... suppression coil. In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A ratio differential relay that detects zero-sequence current from each line on the primary and secondary sides of a three-phase transformer using an operating coil and a suppression coil, and the primary side of the three-phase transformer. A neutral point current detection circuit detects a neutral point current from a neutral point by a coil, and the operating coil and a part of the coil are magnetically harmonically coupled, and the suppressing coil and the other part of the coil are connected to each other. and a zero-sequence current detection circuit on the secondary side of the three-phase transformer of the ratio differential relay and the neutral point current detection circuit are connected in parallel. A transformer ground fault protection device featuring: