JP2004239863A - Grounding method for transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a low resistance is required to be inserted into a transformer ground line to apply a signal voltage for measuring insulation state or insulating of a low voltage electric line, however, a resistor of very large power capacity is required for safe flowing of a current at low-voltage earth fault, and to solve the problem that the earth fault accident in a direct grounding power distribution method which is commonly used is possible to release a large earth fault energy, causing a short circuit fire or electric shock. <P>SOLUTION: A low resistance for applying a voltage for detecting insulation is inserted in a ground line to which one end or a neutral point of a secondary winding of a power distribution transformer is grounded. A means is provided for monitoring a current that flows the resistance. A low-voltage earth fault is recognized when the current flowing it exceeds a single line perfect earth fault current value which is calculated from the constant of a transformer primary power distribution system, and a low-voltage earth fault current limiting resistor is automatically inserted. High-voltage earth fault of primary mixing/contact is recognized when a voltage between a low-voltage electric line and the ground rises to a high voltage which cannot be generated from a low-voltage power distribution, and a low resistance is inserted. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention makes it possible to measure insulation and insulation status in live wires while taking measures against high-low pressure contact accidents, limit unnecessary low-voltage ground fault currents, and reduce failures due to low-voltage ground faults in electrical equipment. In this regard, the present invention relates to a power distribution grounding method for supporting uninterruptible power maintenance and preventing energy loss.
[0002]
[Prior art]
Conventionally, low-voltage power distribution systems have the potential to cause severe accidents such as breakage of low-voltage equipment and electric shocks resulting from breakage of high-voltage or extra-high-voltage electric circuits in transformers or overhead wires due to dielectric breakdown, etc. In order to prevent this, the neutral point or one end of the transformer low-voltage side electric circuit is grounded to the ground with a ground resistance equal to or less than a resistance value calculated so as not to rise above a specified voltage.
[0003]
The grounding resistance value at this time, as the number of weak electrical equipment such as electronics, communication, information, etc. increases, as a countermeasure against obstacles such as noise prevention, the entire building including the iron box of the electric equipment other than the grounding of the electric circuit is made into one same potential body There is a concern that integrated grounding or the like is required, the resistance between the grounding poles approaches zero, and the one-wire complete ground fault current of the low-voltage piezoelectric path sometimes causes a failure near a short-circuit between phases of a power transformer.
[0004]
It is desirable to use a transformer with an anti-touch panel that electrically shields between the primary winding and the secondary winding of the transformer, but it is used in recent industry situations where the cost is high and the cost is low. Less likely to be.
[0005]
In addition, it is not possible to measure the insulation of electric lines and electrical equipment to ground because the electric lines are grounded, so it is impossible to measure them as they are.The electric line is cut off and disconnected from the ground, and all electric lines in the system are measured with an insulation resistance meter. However, maintenance is performed by a low-efficiency insulation resistance measurement method using a low-efficiency insulation resistance meter method, in which a small portion with poor insulation is specified and sorted.However, this method cannot predict or prevent insulation deterioration accidents that occur during use. Can not.
There is a live-line insulation monitoring system that inserts a low-impedance transformer into the ground wire and applies an AC voltage for monitoring the insulation between the electrical circuit and the ground, but the AC frequency range is limited to the range where the transformer can be used For this reason, there is a problem in that an influence of an electric circuit loss, a noise frequency generated by a semiconductor power element, or the like is displayed unnecessarily, and an indication of insulation deterioration appears.
In order to perform measurement close to DC insulation resistance, it is necessary to lower the AC frequency for insulation detection, but superposition application of the measurement signal voltage must be performed by a resistor. However, considering the current at the time of a touch accident and at the time of a low-voltage ground fault, the resistor becomes a huge resistor of several tens of kW, and its practical use has been difficult.
[0006]
[Problems to be solved by the invention]
With the increase in power loads, such as information processing, communication, and sequence equipment in daily life, where power outages are difficult, it has become extremely difficult to measure with an insulation resistance meter after a power outage. Because of the difficulty of power outages, many people have reluctantly lost measurement opportunities for many years.
The present invention provides a practical small-capacity insulation monitoring voltage superimposing resistor that enables the use of a hot-line insulation monitoring device or a hot-line insulation condition monitoring device, and enables insulation or insulation of an electric circuit without a power failure. Provide a safe way to measure state more accurately. According to this, the selection of insulation or poor insulation conditions can be rationalized by tracing the current attributable to insulation deterioration to the downstream of the electrical circuit with a measuring instrument and inevitably reaching the equipment with poor insulation. This will help to significantly improve electrical security efficiency.
[0007]
In addition, if grounding is performed to suppress the rise of the ground voltage of the secondary low-voltage distribution system due to contact between the primary and secondary, the low-voltage ground-fault current will increase and the leakage fire and ground fault will increase compared to the non-grounding method. there were.
In the present invention, a large current at the time of a low-voltage ground fault is detected, and a low-voltage ground fault is distinguished from a high-voltage primary contact, and a low-voltage ground fault is automatically inserted to limit a fault current. The effect of reducing the loss is great.
[0008]
[Means for Solving the Problems]
FIG. 1 is an explanatory diagram of the present invention. A low resistance 21 for applying a voltage for measuring the insulation or insulation state of the low-voltage circuit on the hot wire is inserted into the ground line circuit 3 for grounding the neutral point or one terminal of the low-voltage winding 2 of the transformer.
This resistance value is such that if the high-voltage or extra-high-voltage circuit breaks the insulation of the transformer, etc., and touches, the rise in the low-voltage side to ground voltage will not be an obstacle even if the ground resistance value of the grounding work 4 is included. The resistance value is small enough to superimpose and apply a signal voltage for measuring the insulation or insulation state of the low piezoelectric path.
[0009]
The electric circuit connected to the resistor 21 is provided with a low-voltage ground fault separation circuit breaker 22 that measures a passing current and cuts off the circuit when the current exceeds a low-voltage ground fault separation current value.
As a low-voltage ground fault separation / breaking device, a thermal or electromagnetic overcurrent breaker, a fuse, a semiconductor switch, or the like can be used.
An electric contact 25 is provided for transmitting a state as an alarm to the outside when the interruption is performed. This can be by other communication means.
[0010]
A low-voltage ground-fault current limiting resistor 29 is provided in parallel with the resistor 21. When the low-voltage ground fault separation circuit breaker 22 operates, the low-voltage ground fault current is limited, the low-voltage ground fault current is reduced, and the fault due to the low-voltage ground fault is reduced. To provide an efficient ground fault current.
[0011]
When the voltage between the neutral point of the transformer and the ground or between the terminals of the resistor 29 reaches a high voltage that does not normally occur in the secondary low-voltage circuit, the primary contact of the transformer is identified, and the low-resistance 21 Circuits 26, 27 and 28 for releasing and restoring the circuit breaker 22 are provided.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Since the present invention is configured as described above, in a normal state, a DC or AC insulation monitoring voltage 30 is applied to the parallel portion of the resistor 21 and the resistor 29 to measure the live insulation of the low piezoelectric path including the load equipment and to monitor the insulation state. Such as measurement diagnosis. Also, even if a primary-secondary contact fault occurs due to transformer insulation breakdown, the current value of the resistor 21 and its low-voltage ground fault separation is a one-wire complete ground fault current determined by the constant of the transformer primary distribution system. Since the standard is set, security can be sufficiently secured.
When the low-voltage ground fault current exceeds the primary system one-line complete ground fault current determined by the constant to ground of the primary power distribution system and reaches the low-voltage ground fault separated current value, the low-voltage ground fault separation monitoring device 23 identifies the low-voltage ground fault, The low resistance 21 is disconnected from the circuit by the cutoff devices 24,22.
[0013]
Since the low-resistance 21 is cut off, the low-voltage ground-fault current limiting resistor 29 is enabled, and the ground-fault current is limited to a current that is efficient for a designed ground-fault location search even at a complete ground-fault.
Since this resistor consumes low-voltage ground fault voltage, the rise of contact voltage at insulation degradation is also reduced, and in addition to the reduction of fires, electric shocks and electrical disturbances due to leakage power, the operation of receiving the leakage relay of low-voltage equipment that frequently occurs in recent years It is also effective in reducing the amount of water.
[0014]
Even at the time of low-voltage ground fault, even if there is a touch accident between the primary and secondary transformers, grounding is performed at the low-voltage ground fault point, and the rise in ground voltage is small.
[0015]
If the low-voltage ground fault is restored and the low-resistance 21 circuit breaker 22 is not restored and the primary-secondary contact between transformers occurs, the voltage between the neutral point or one end of the secondary transformer and the ground When the voltage reaches a high voltage which cannot be generated in the secondary low-voltage circuit set in the primary contact separation monitoring circuit 26, the primary contact separation monitoring cutoff devices 27 and 28 are instantaneously activated, and the low-resistance circuit breaker 22 is restored. The rise in the ground voltage can be suppressed within the design value.
[0016]
【Example】
FIG. 1 shows an embodiment of the present invention. 1 is a primary winding of a distribution transformer, 2 is a secondary winding, 3 is a neutral grounding line of the transformer, and 4 is grounding. Reference numeral 5 denotes a ground resistance between a grounding electrode 6 such as an iron box or a building of an electric machine and a grounding electrode 4 at a neutral point of a transformer. Reference numerals 7, 8, and 9 denote terminal blocks for grounding wires. Reference numeral 10 denotes a ground capacitance as a distribution constant that determines a one-line ground fault current of the transformer primary distribution system. 11 is a contact resistance due to insulation breakdown between the primary and the secondary of the transformer. The ground fault current of the primary power distribution system which has entered from now on is the one which flows to the neutral point ground line 3 and the low-voltage ground fault resistor 16 if there is one. Each of the components is divided into shunt components 13, but all of them return to the constant 10 of the primary power distribution system of the transformer through the ground.
[0017]
Reference numeral 15 denotes an iron box of an electric machine or a grounding structure of a building. A low-voltage ground fault current 17 passes through the ground via a ground fault resistor 16 and is shunted to the resistors 21 and 29 of the present invention, and is returned to the neutral point of the transformer.
[0018]
Reference numeral 30 denotes an example of an insulation detection voltage applied to the insulation detection voltage application resistor of the present invention, and it is also possible to apply a direct current.
[0019]
The part surrounded by the two-dot chain line 20 is a part constituting the present invention. Reference numeral 21 denotes a low resistance for applying a hot wire insulation detection voltage. The circuit breaker 22 is a breaking contact operated by a low-voltage ground fault separated current monitoring device 23 and its output relay winding 24, and 25 is an alarm contact for transmitting the operation to the outside. Reference numeral 26 denotes a primary contact separation monitoring device for monitoring an increase in low-voltage side voltage caused by contact of the primary system. Reference numeral 27 denotes an output relay winding, and reference numeral 28 denotes a contact for restoring the circuit breaker 22 operated by 27.
[0020]
Since the circuit breaker 22 is normally closed, a parallel combined resistance of the resistors 21 and 29 is inserted into the ground line 3 of the transformer. When an accident such as a transformer touch occurs and a primary voltage is applied to the secondary winding, a current 12 caused by the primary voltage flows through the combined resistance. The low resistance 21 is set in advance to a sufficiently low resistance value even with the addition of the ground resistance 4 in a one-wire complete ground fault current in consideration of the ground constant of the primary power distribution system. The rise is below the specified design value.
[0021]
When the low voltage side insulation breaks down and the ground insulation resistance 16 extremely lowers to zero and a low voltage one-wire complete ground fault occurs, the low voltage ground fault current 17 due to this causes the ground fault resistance 16 and the ground electrode 6 of the grounding structure. A current is determined by the resistance 5 between the transformer and the ground electrode 4 of the transformer, the combined resistance of 21 and 29 inserted according to the present invention, and the impedance of the transformer and wiring. This current reaches several hundred A in the case of a structure equipotential grounding structure or the like. The resistor 21 has a structure having a power capacity to withstand this current for a short time. Note that the resistor 29 consumes several tenths of the power of the resistor 21.
[0022]
When a low-voltage ground fault occurs, 23 and 24 operate in cooperation with each other to detect a voltage drop generated in the combined resistance of 21 and 29, open the cutoff device 22, and disconnect the resistance 21 from the system. Due to this, the low-voltage ground fault current limiting resistor 29 becomes effective and limits the low-voltage ground fault current to a design current value that is efficient for low-voltage ground fault detection. At this time, since the voltage drop becomes the resistance 29 alone, the voltage rises greatly to ensure the operation.
[0023]
In conjunction with this, the low-voltage ground fault alarm contact 25 is closed to warn of the occurrence of a serious ground fault.
[0024]
When the low-voltage ground fault disappears, the voltage drop of the resistor 29 also decreases. When the voltage drops below the restoration voltage set value of the low-voltage ground separation circuits 23 and 24, the shutoff device 22 is closed again and returns to the normal state.
[0025]
Reference numeral 8 denotes a short-circuiting piece provided on the grounding terminal block, which is connected when the present invention is not used to establish a direct grounding as in the past. In this case, the secondary grounding complete ground fault current reaches several thousand amps. There is. Reference numeral 30 denotes an example of a connection for applying an insulation monitoring AC voltage to the insulation monitoring voltage superimposed resistor of the present invention. Since the resistance 21 is not affected by frequency, it can be used for any frequency of insulation from DC to AC and for measuring the insulation state. Can respond.
[0026]
【The invention's effect】
As described above, in the grounding method to which the present invention is applied, in the case where the current of the primary-secondary contact fault of the transformer with relatively small current is detected in the low resistance 21 and the large current which is clearly recognized as the low voltage ground fault is detected. Is configured so as to flow separately to the current limiting resistors 29, so that equipment can be manufactured inexpensively with practically small-capacity resistors.
In addition, the use of this superimposed resistor allows the practical application of an insulation detection method using direct current or ultra-low frequency, so that monitoring and diagnosis of live-line insulation can be utilized as familiar items.
[0027]
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Primary high voltage winding of transformer 2 Secondary low voltage winding of transformer 3 Grounding line 4 connecting neutral point of low voltage winding and grounding electrode 4 Primary secondary contact accident protection connected to neutral point of transformer The ground electrode 5 of the ground electrode 4 and the resistance between the ground electrode 6 6 The ground electrode 7 of an iron box of an electric machine, an electric facility, a building, etc. 7 The terminal 8 for connecting the present invention The terminal is short-circuited when the present invention is not used. 9 Short-circuiting piece 9 Grounding terminal block of iron box of electric machine or building grounding structure 10 Equivalent ground capacitance of transformer primary distribution system 11 Contact resistance between transformer primary and secondary 12 In case of primary secondary contact accident Primary ground fault current from the neutral point of the secondary winding to the ground via the present invention. Composite value of system ground fault currents 12 and 13 15 Iron box of electric machinery and equipment and building grounding structure 16 Ground fault resistance 17 generated in low-voltage distribution system 17 Low-voltage ground fault current 20 generated by low-voltage winding 2 Two-dot chain line box is a component of the present invention 21 A circuit breaker that cuts off low resistance 22 21 that applies a signal voltage for detecting live-line insulation. 23 A low-voltage ground fault separation monitoring device 24 for monitoring the current flowing into 21 21 An output relay of the 23 23 An alarm contact 26 for notifying the operation of the winding wire 25 22 Primary contact for monitoring the voltage between the secondary neutral point of the transformer and the ground Contact 29 for restoring the breaker of the output relay winding 28 22 of the separation monitoring device 27 26 Low-voltage ground fault current limiting resistor 30 An example of the insulation detection signal voltage generator connected to the present invention

Claims (3)

In the grounding circuit of the secondary winding of the transformer, a low-voltage ground fault is identified by detecting a ground-fault current that exceeds the one-wire complete ground-fault current determined by the ground constant of the primary power distribution system, and a low-voltage ground-fault current limiting resistor Is inserted between the ground point of the transformer and the ground to detect a high voltage that cannot be generated on the secondary low-voltage path of the normal transformer to identify the contact between the primary and secondary transformers and to identify the secondary neutral point. Or, a method of grounding a transformer having one end connected to a low resistance or directly grounded. A low-resistance resistor for applying an insulation detection signal and a low-voltage ground fault current limit to the ground wire circuit that grounds the neutral point or one end of the low-voltage distribution transformer to protect against primary voltage contact. Insert a resistor, and always operate a low-resistance resistor corresponding to a contact fault.When a large current is detected on the ground wire and a low-voltage ground fault is identified, a low-voltage ground fault current limiting resistor is activated. A method for grounding a transformer, characterized in that it operates. When the secondary voltage of the transformer's neutral point exceeds the maximum ground voltage of the secondary system that normally occurs, it is identified that the primary high voltage system is touching, and the secondary ground voltage rise due to the entry of the primary ground fault current is detected. A transformer grounding scheme configured so that a low resistance intended to be reduced to within a predetermined value is inserted.

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