JP5643592B2 - Protective relay - Google Patents

Description

  Embodiments of the present invention relate to a protective relay.

  Conventionally, a protective relay is used to determine the presence or absence of a grid fault in the power system and to determine the operation of a circuit breaker installed in the grid fault section. This protective relay goes through a current transformer that converts the magnitude of the input current and an analog conversion circuit that converts the signal on the secondary side of the current transformer to a predetermined level, and then A / D converts by the A / D conversion circuit. doing. Furthermore, the operation is determined by taking it into the arithmetic processing circuit as a digital signal and performing predetermined arithmetic processing in the arithmetic processing circuit.

  The current transformer that converts the magnitude of the input current increases the core cross-sectional area of the current transformer and the secondary winding in order to prevent saturation of the current transformer when a system fault current including a DC component flows. Current transformer saturation characteristics were improved by increasing the number of turns and the cross-sectional area of the secondary winding. However, these saturation measures have the problem of causing an increase in the size of the current transformer.

  In addition, in the conventional protective relay, in order to prevent erroneous determination due to current transformer saturation, the amplitude of each positive and negative wave of the digital signal after A / D conversion is determined by the analog conversion and arithmetic processing circuit of the protective relay However, it may not be possible to correctly determine the operation with a grid fault current that includes a DC component such that one of the positive or negative waves exceeds the full scale value. there were.

JP 2009-201209 A

  As described above, there is a problem that the current transformer increases in size in order to prevent current transformer saturation when a system fault current including a direct current component flows. Furthermore, the erroneous determination prevention measure at the time of current transformer saturation by the arithmetic processing may not be able to correctly determine the operation with an accident current in which one of the positive wave and the negative wave exceeds the full scale value.

  An object of the present invention is to provide a protective relay capable of accurately determining an operation even when a system fault current including a direct current component flows.

A protective relay according to an embodiment of the present invention includes an input current transformer that converts the magnitude of an input current and outputs the converted signal as an analog signal, and an analog signal output from the input current transformer. An analog conversion circuit for converting into an analog signal, an A / D conversion circuit for converting a predetermined analog signal converted by the analog conversion circuit into a digital signal, and an arithmetic process based on the digital signal converted by the A / D conversion circuit In a protective relay comprising an arithmetic processing circuit to be performed and a relay output circuit that operates a contact output according to an arithmetic result of the arithmetic processing circuit , the analog conversion circuit converts the analog signal output from the input current transformer into a negative resistance Circuit and the power booster circuit, and the power booster circuit is used when the analog signal output from the negative resistance circuit is positive. A first transistor that increases the intensity of the positive analog signal and outputs it to the analog conversion circuit, and an analog signal that increases the intensity of the negative analog signal when the analog signal output from the negative resistance circuit is negative. And a second transistor that outputs to the conversion circuit .

The block diagram which shows the structure of the protection relay in 1st Embodiment. The figure which shows the equivalent circuit of the input current transformer 1 in 1st Embodiment. The figure which shows the equivalent circuit of the negative resistance circuit 8 in 1st Embodiment. The figure which shows the equivalent circuit of the negative resistance circuit 8 and the power booster circuit 29 in 1st Embodiment. The figure which shows the equivalent circuit of the negative resistance circuit 8 to which the thermistor 30 in 2nd Embodiment is applied.

  A protective relay according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
The configuration of the protective relay according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the protective relay. The protective relay includes an input current transformer 1, a negative resistance circuit 8, an analog conversion circuit 2, an A / D conversion circuit 3, an arithmetic processing circuit 4, a relay output circuit 5, and a contact output 6.

  The magnitude of the input current is converted by the input current transformer 1, and the current waveform captured at a predetermined current ratio is transmitted as an analog signal to the analog conversion circuit 2 via the negative resistance circuit 8.

  The analog conversion circuit 2 includes an analog prefilter, an operational amplifier, and the like, and removes high frequency contained in the analog signal input from the negative resistance circuit 8 and converts the signal intensity to a predetermined value. Further, a predetermined analog signal from which the high frequency is removed and the signal intensity is converted to a predetermined value is output to the A / D conversion circuit 3.

  The A / D conversion circuit 3 converts the predetermined analog signal input from the analog conversion circuit 2 into a digital signal, and outputs the digital signal to the arithmetic processing circuit 4.

  The arithmetic processing circuit 4 performs arithmetic processing for determining the operation of a circuit breaker (not shown) based on the digital signal input from the A / D conversion circuit 3, and outputs the arithmetic result via the relay output circuit 5 as a contact output. 6 is output.

  The contact output 6 is connected to a circuit breaker (not shown), and operates the circuit breaker based on a calculation result input from the arithmetic processing circuit 4 of the protective relay through the relay output circuit 5.

  Next, the configuration of the input current transformer 1 will be described with reference to FIG. FIG. 2 is an equivalent circuit showing the configuration of the input current transformer 1 and the negative resistance circuit 8.

An input current I ₁ flows from the input terminal 9 to the input terminal 10, and a magnetic flux φ is generated in the iron core of a current transformer (not shown) by the current transformer primary winding 11, and the current transformer secondary winding 12 is generated by the magnetic flux φ. An induced voltage E ₂ is generated, and a current I ₂ flows to the current transformer secondary side. Upon deriving the saturation current equation for calculating the current transformer for indicating the current transformer saturation characteristics, current transformer input impedance Z _in and the current transformer saturation when the input voltage E _m the formula (1), equation (2), It shows in Formula (3).

The current transformer input impedance Z _in is the current transformer primary winding resistance 16, the current transformer secondary winding resistance 17, the current transformer secondary load impedance 21, the current transformer primary winding frequency 18, the current transformer secondary. The number of windings 19 is expressed as in equation (1).

Input voltage E _m at current transformer saturation, the change of the magnetic flux φ generated in the current transformer core, shown from the current transformer primary windings N ₁ as equation (2), also the current transformer input impedance Z _{From in} and the current transformer saturation current I _ma , it is expressed as in equation (3).

Furthermore, the current transformer saturation current I _ma is expressed by the equation (4) from the equations (1), (2), and (3).

(A typical current transformer is negligible with a current transformer primary winding resistance r ₁ ≈0.)
here,
I _ma : Current transformer saturation current (A _rms )
E _m : Input voltage at the time of current transformer saturation (V _rms )
ω: angular frequency (rad / s)
f: Input frequency (Hz)
N ₁ : Number of turns of the current transformer primary winding 18 (T)
N ₂ : Number of turns of current transformer secondary winding 19 (T)
S: Iron core cross-sectional area (cm ² )
B _m : Maximum magnetic flux density (Wb / m ² )
φ: Magnetic flux generated by current transformer core (Wb)
Z _in : Current transformer input impedance (Ω)
r ₁ : resistance value of the current transformer primary winding resistance 16 (Ω)
r ₂ : Resistance value of the current transformer secondary winding resistor 17 (Ω)
Z _L : Resistance value of the current transformer secondary load impedance 21 (Ω)
It is said.

As shown in the equation (4), in order to increase the current transformer saturation current I _ma , the current transformer primary winding number N ₁ is decreased, the current transformer secondary winding number N ₂ is increased, the iron core breakage the area S is increased, it adopts a high iron core of maximum magnetic flux density B _m, to reduce the current transformer secondary winding resistance r _2, there is a method of reducing the secondary load impedance Z _L current transformer. Here, by providing the negative resistance circuit 8 in the protective relay, the current transformer secondary winding resistance 17 is reduced, and the current transformer saturation current _Ima is increased.

  Next, the configuration of the negative resistance circuit 8 in the protective relay will be described with reference to FIG. FIG. 3 is an equivalent circuit showing the configuration of the negative resistance circuit 8. The negative resistance circuit 8 includes resistors 22, 23 and 24 and an operational amplifier 25.

Voltage V _i which is input to the negative resistance circuit 8, the voltage V ₀ which is output from the current flowing through the current transformer secondary side and the resistance 22, 23 and 24 a negative resistance circuit 8 (5), ( 6).

Equation (5), the voltage _{V o} output from the negative resistance circuit 8 (6) given in equation (7).

Voltage V _i which is input to the negative resistance circuit 8 Substituting equation (7) into equation (6) is given by Equation (8).

Combined impedance r ₃ of the negative resistance circuit 8 from equation (8) will have a negative resistance value indicated by the equation (9). As shown in FIG. 3, since the negative resistance circuit 8 is installed, the current transformer secondary winding resistance 17 can be canceled by the combined impedance 26 of the negative resistance circuit 8 having a negative resistance value.

here,
V _i : Voltage input to the negative resistance circuit 8 (V _0P )
V _o : voltage output from the negative resistance circuit 8 (V _0P )
I ₂ : Current flowing in the secondary side of the current transformer (A _0P )
Z ₁ : resistance value of the resistor 22 (Ω)
Z ₂ : resistance value of the resistor 23 (Ω)
Z ₃ : resistance value of the resistor 24 (Ω)
r ₃ : Composite impedance 26 (Ω) of the negative resistance circuit 8
It is.

  Next, a selection example of the resistor 22, the resistor 23, the resistor 24, and the operational amplifier 25 when a system fault current including a direct current flows to the current transformer will be described.

When the DC current is 100% superimposed, the current transformer secondary current I _2ad is expressed as shown in the equation (10) from the system _fault current I _1ad , the current transformer primary winding number 18 and the current transformer secondary winding number 19. It is.

Grid _fault current I _1ad = 100 A _rms , grid frequency f = 50 Hz, current transformer saturation current I _ma = 180 A _rms , current transformer primary winding number N ₁ = 1 T, current transformer secondary winding number N ₂ = 3000 T, variable Assuming that the current transformer secondary winding resistance r ₂ = 210Ω and the current transformer secondary load impedance Z _L = 10Ω, the change when the system _fault current I _1ad flows to the primary side of the current transformer from Equation (10). The current flowing through the secondary side I _2ad ≈94.3 mA _0P .

Here, in order to prevent DC current saturation of the current transformer, the concept of designing so that the DC current is taken into consideration and the saturation current without DC superposition is increased by an oversize factor K times is introduced, and the current transformer is not saturated. In this case, the current transformer secondary side voltage E _{2 ′} is calculated. The oversize factor K is expressed as shown in Equation (11).

here,
K: Oversize factor ω: Angular frequency (rad / s)
T: Expected non-saturation time (ms)
It is.

When the saturation time T is set to the saturation time T = 15 ms that allows the peak value detection type (peak value detection type) calculation processing, the oversize factor K≈5.71 from Expression (11). The saturation limit current I _mda that does not saturate even if the DC current is 100% superimposed is given by the equation (12) from the current transformer saturation current I _ma and the oversize factor K expressed by the equation (11).

From equation (12), the saturation limit current I _mda ≈31.5 A _rms that does not saturate even when the direct current is superimposed 100%.

Here, when the saturation limit current I _mda that does not saturate even if the DC current obtained as described above is superimposed 100% is considered as the system _fault current I _1ad , the equation (10) can be converted into the equation (13). Further, the current transformer secondary side voltage E _{2 ′} at this time is the current transformer secondary current I _{2ad ′} when the saturation limit current I _mda flows in the current transformer primary side, the current transformer secondary winding. From the resistor 17 and the current transformer secondary load impedance 21, the following equation (14) is obtained.

From equation (13), when the saturation limit current I _mda flows on the primary side of the current transformer, the current transformer secondary side current I _{2ad ′} ≈29.7 mA _0P , and the saturation limit current I _mda is on the primary side of the current transformer. From the current transformer secondary side current I _{2ad ′ in} the case of current flow and the equation (14), the current transformer secondary side voltage E _{2 ′} at the time of saturation of the current transformer becomes 6.5V _0P , which is the current transformer secondary side. Shows the voltage values that can be generated.

Here, using the current transformer secondary current I _2ad and the combined impedance 26 of the negative resistance circuit 8 when the _{grid fault} current I _1ad flows on the primary side of the current transformer, the equation (14) is expressed by the equation (15). Can be converted as follows.

Further, the transformer secondary side current I _2ad when the negative resistance circuit 8 is provided from the equations (14) and (15) is represented by the following equation (16).

Further, when the equation (16) is substituted into the equation (13), the saturation limit current I _mda when the negative resistance circuit 8 is provided can be shown as shown in the equation (17).

Here, in order to select the constant of r ₃ so that r ₂ + Z _L > r ₂ + r ₃ , when the negative resistance circuit 8 is provided, only (r ₂ + Z _L ) / (r ₂ + r ₃ ) is saturated. The limit current I _mda can be increased.

Current transformer secondary winding is a current transformer secondary current I _2ad and conditions when the calculated current transformer secondary voltage grid fault current I _1ad the E _{2 'and} current transformers primary flows If the resistance r ₂ is substituted into the equation (15), the combined impedance r ₃ of the negative resistance circuit 8 ≈−141Ω, and further substituted into the equation (9), the resistance Z ₁ = 10Ω, the resistance Z ₂ = 20 kΩ, the resistance Z A result of ₃ = 280 kΩ is obtained. As a result, when the negative resistance circuit 8 is provided, the saturation limit current I _mda ≈99 A _rms , and the saturation limit current can be improved by about 3.14 times compared to the case where the negative resistance circuit 8 is not provided.

The operational amplifier 25 used for the negative resistance circuit 8 has a voltage V _{o ≈14V 0P} output from the negative resistance circuit 8 based on the parameters of the resistors 22, 23, and 24, and a grid _fault current I _1ad on the primary side of the current transformer. From the current transformer secondary current I _2ad ≈ 94.3 mA _{0P when the} current flows, the power supply voltage of the operational amplifier 25 is ± 15 V or more, and the output current of the operational amplifier 25 is 94.3 mA or more, as in OPA551 (TEXAS INSTRUMENTS) Adopt an op amp.

Next, the case where an operational amplifier with a limited output current is employed will be described with reference to FIG. FIG. 4 is a diagram for compensating for the shortage of output current of the negative resistance circuit 8 by the power booster circuit 29. 6, the current output from the operational amplifier 25, poured into the base terminal of the npn-type transistor 27 or the pnp transistor 28, the collector current of the current amplification factor _h npn type amplified by the _FE transistor 27 or the pnp transistor 28 A current I _{2 ′} that is an emitter current can flow from the base current.

As described above, when the negative resistance circuit 8 is provided, the saturation current can be increased by (r ₂ + Z _L ) / (r ₂ + r ₃ ) as compared with the case where the negative resistance circuit 8 is not provided. The effect of improving the current transformer saturation characteristics can be obtained without changing the shape and material of the current transformer. Further, by improving the current transformer saturation characteristics, it is not necessary to perform special calculation processing such as saturation determination, and the effect of reducing the calculation burden can be obtained.

(Second Embodiment)
The protection relay according to the second embodiment will be described with reference to FIG. The configuration of this embodiment is different from that of the first embodiment in that an NTC thermistor 30 is added to the negative resistance circuit 8.

  The NTC thermistor 30 is connected in series with the resistor 23 and has a negative temperature coefficient so that the resistance decreases as the temperature rises.

The secondary winding of a typical current transformer uses copper with low resistance. Since the temperature coefficient α of copper is 0.43 [% / ° C.] and the expected current transformer secondary winding resistance r ₂ changes due to temperature fluctuation, the expected saturation limit current I _mda is not _achieved . Therefore, an NTC thermistor 30 having a negative temperature coefficient is connected in series with the resistor 23 of the negative resistance circuit 8. Combined impedance r ₃ of the negative resistance circuit 8 at this time is represented by equation (18).

here,
Z ₁ : resistance value of the resistor 22 (Ω)
Z ₂ : resistance value of the resistor 23 (Ω)
Z ₃ : resistance value of the resistor 24 (Ω)
Z ₄ : Resistance value of the NTC thermistor 30 (Ω)
r ₃ : resistance value (Ω) of the combined impedance 26 of the negative resistance circuit 8
It is.

According to this embodiment, since the NTC thermistor 30 has a negative temperature coefficient in addition to the effects of the first embodiment, the current transformer secondary winding resistance r ₂ due to the temperature coefficient of the current transformer secondary winding. it is possible to vary the absolute value of the combined impedance r ₃ of the negative resistance circuit 8 in the same direction as the direction of the change can be a saturation limit current I _mda expect even if there are temperature fluctuations.

  According to the embodiment of the present invention, it is possible to provide a protective relay that can accurately determine operation even when a system fault current including a direct current component flows.

  As mentioned above, although some embodiment of this invention was described, these embodiment was shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1: Input current transformer 2: Analog conversion circuit 3: A / D conversion circuit 4: Arithmetic processing circuit 5: Relay output circuit 6: Output contact 8: Negative resistance circuit 9: Input terminal 10: Input terminal 11: Current transformation Current transformer primary winding 12: Current transformer secondary winding 14: Output terminal 15: Output terminal 16: Current transformer primary winding resistance 17: Current transformer secondary winding resistance 18: Current transformer primary winding number 19: Current transformer secondary winding number 20: Current transformer secondary excitation impedance 21: Current transformer secondary load impedance 22: Resistor 23: Resistor 24: Resistor 25: Operational amplifier 26: Composite impedance 27 of negative resistor 8: npn type Transistor 28: pnp type transistor 29: Power booster circuit 30: NTC thermistor

Claims (5)

An input current transformer that converts the magnitude of the input current and outputs it as an analog signal;
An analog conversion circuit that converts the analog signal output from the input current transformer into a predetermined analog signal indicating a predetermined analog signal;
An A / D conversion circuit for converting a predetermined analog signal converted by the analog conversion circuit into a digital signal;
An arithmetic processing circuit that performs arithmetic processing based on the digital signal converted by the A / D conversion circuit;
A relay output circuit that operates a contact output in accordance with a calculation result of the arithmetic processing circuit;
In a protective relay comprising:
The analog conversion circuit receives the analog signal output from the input current transformer through the negative resistance circuit and a power booster circuit,
The power booster circuit includes: a first transistor that increases the strength of the positive analog signal when the analog signal output from the negative resistance circuit is positive; And a second transistor that increases the strength of the negative analog signal and outputs the analog signal to the analog conversion circuit when the analog signal output from the resistive circuit is negative .   The protective relay according to claim 1, wherein the negative resistance circuit includes an operational amplifier and a plurality of resistors. The negative resistance circuit, protective relay of claim 1 or 2, wherein comprising a thermistor having a temperature coefficient of the negative. The protective thermistor according to claim 3 , wherein the thermistor is connected in series with a resistor constituting the negative resistance circuit. The protective thermistor according to claim 3 or 4 , wherein the thermistor compensates for a change in a resistance value of the input current transformer winding accompanying a temperature change.

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