JPH0514501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a protective relay device for an unbalanced load in a three-phase AC circuit, for example, a three-phase circuit whose load is an induction motor.

[Background of the invention]

For example, a protective relay that takes unbalanced loads into account has been proposed, such as Japanese Patent Publication No. 47-582, which immediately detects even a minute current when the unbalance is at its maximum, that is, when a phase is lost. For this reason, even in an unbalanced state where the unbalance rate is less than the generally allowable unbalance rate of about 10%, the operating current decreases, resulting in a drawback that the load cannot fully demonstrate its capacity.

To explain this more specifically, in the known device, when the load is balanced, an output is generated if the load current exceeds the reference value of the minimum setting reference value generator 5, and when the load is unbalanced, the output is generated by the amount of current equivalent to each phase and the minimum standard value. A comparator 6 compares and detects the smallest of the quantities (ie, the output of the minimum value selection circuit 4) and the largest of the phase current quantities (ie, the output of the maximum value selection circuit 3). Therefore, in the unbalanced state, the comparator 6 generates an output with a smaller load current than in the balanced state. for example,
When unbalance is at its maximum (phase loss), even the smallest current is immediately detected and output. This characteristic is that in a balanced load, the setting value at equilibrium is 100% determined by the reference value of the minimum setting reference value generator 5, and as the unbalance rate increases, the operating current decreases, and at 100% unbalance. It will operate with a very small current.

This method uses a generally accepted unbalance factor of 10
Even if the unbalance is less than about %, the operating current will drop and the load will not be able to fully demonstrate its capacity.
Taking the case of a three-phase induction motor as an example, even if one phase is open and the unbalance rate becomes 100%, if the current at this time is several tens of percent of the rated current, overheating, burnout, etc. Conventional protective relays have the problem of immediately cutting off the load, even though they can continue operating without causing any abnormalities.

[Purpose of the invention]

An object of the present invention is to provide a protective relay device that can provide reasonable protection in the event of unbalance.

[Summary of the invention]

The present invention does not judge the necessity of protection only based on the maximum and minimum deviation of each phase current, that is, the unbalance, but takes into account both the magnitude of the unbalance and the magnitude of the balanced value of the load current. The necessity of protection will be determined based on the following criteria.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
1 is a feeder, and 2 is a protected load, such as an induction motor. 3 is a current deriving section, which is composed of a current transformer CT, a diode D, resistors _R1 , _R2 , and a capacitor _C1 . 5 is a current adjustment/subtraction smoothing unit, into which the current detection output of each phase and the output of an unbalance detection unit 23 (described later) are introduced via a resistor R ₃ , and a resistor R ₄ , R ₅ , a capacitor C ₂ , and an operational amplifier. It is smoothed by a filter circuit consisting of _OP1 . The output of OP ₁ is a variable resistor
VR ₁ , resistors R ₆ to R ₁₀ , and switches SW ₁ to _{SW 4} , any one of which is selectively closed, are used in the gain adjustment circuit to obtain an output of a predetermined magnitude for a predetermined input magnitude. Corrected and output.
7 is a first reference value generating section, which includes a variable resistor VR ₂ ,
Consists of resistor R ₁₁ . The current smoothing unit 5 and the reference value generating unit 7 are configured to output voltages of the same magnitude and opposite polarity, for example, when the load 2 is operated in a rated state with a balanced load. 9 is a difference calculation section, which includes resistors R ₁₂ , resistors R ₁₃ , R ₁₄ and a calculation amplifier.
Consists of OP ₂ . The differential voltage between outputs 5 and 7 introduced through resistor _R12 is output. 11 is a proportional-integral calculation section, which includes a variable resistor VR ₃ and a resistor R ₁₅
~R ₁₈ , a capacitor C ₃ , a diode D ₁₁ , and an operational amplifier OP ₃ . The calculation unit 11 is
It is possible to obtain an output that is the sum of the magnitude proportional to the input and the magnitude obtained by integrating the input over time. 13 is the second
It is a reference value generation section, and includes a diode D ₁₃ , a resistor R ₁₉ ,
and variable resistor VR ₄ . Reference numeral 15 denotes a comparison section, which is composed of R ₂₀ , R ₂₁ , a diode D ₁₅ , and an operational amplifier OP ₄ . The outputs of the arithmetic unit 11 and the reference value generating unit 13 are introduced via the resistor R ₂₀ , and when the difference between these exceeds a predetermined value determined by the resistors R ₂₀ and R ₂₁ , an output is obtained. 17 is the output section, which includes resistor R ₂₅ , transistor Q, auxiliary relay R _Y , diode D ₁₇ and issuing diode LED
It becomes more. When the output from the comparator 15 is obtained via the resistor R ₂₅ , the relay R _Y is operated,
Make the LED emit light. 19 is the power supply section, and the resistor
R ₂₆ , capacitor C ₄ , diode D, capacitor
C ₅ , resistors R ₂₇ , R ₂₈ and Zener diode
Consists of ZD ₁₉ to _{ZD 21} . A common potential COM, + power supplies P ₁₀ , P ₁₄ and - power supplies N ₁₀ are output as outputs, and these are connected to power lines indicated by the same symbols in each part. Reference numeral 21 denotes a current maximum value detection section, into which each phase current obtained by the current derivation section 3 is introduced. Each phase current is compared by a comparison circuit consisting of resistors R ₃₁ , R ₃₂ , R ₃₃ diodes D ₃₁ , D ₃₂ capacitor C ₆ and operational amplifier OP ₅ , and the maximum value thereof is derived. Reference numeral 23 denotes an unbalance detection section, into which the maximum value is introduced together with each phase current. Resistors R ₃₄ , R ₃₅ , R ₃₆ , R ₃₇ , capacitor C ₇ , diode D ₃₃ and operational amplifier OP ₆
When the load current is balanced, the output is 0, and when the load current is unbalanced, an output corresponding to the unbalance is obtained. The size of the output of the maximum value detection section 21 can be selected by considering the balance of the entire circuit, but for example, when the currents of each phase are balanced, the size of the output of the maximum value detection section 21 should be three times this value, and the current of each phase It is also good to make it equal to the sum of . D ₃₄ is a diode, R ₃₈ , R ₃₉
are resistors, and these are circuits for outputting an unbalanced output of current to the current addition/balancing section. resistance
The voltage obtained at R ₃₉ is amplified through the resistor R ₃ .
Added to OP ₁ . ZD ₂₃ is a Zener diode,
R ₄₀ is a resistor, P is a transistor, and these are circuits for detecting that the unbalanced output of the current exceeds a predetermined value. When the unbalanced output exceeds a predetermined value, transistor P turns on,
Since the variable resistor VR ₄ of the second reference value generating section 13 is short-circuited, the criterion for determining whether or not a relay output is necessary becomes small.
Since the current addition and smoothing unit 5 adds the currents of each phase and the unbalanced output, the difference calculation unit 9 outputs the difference between these added signals and the reference value. In other words, according to this embodiment, the necessity of protection is not determined only based on the large current of each phase or only on the large unbalanced output, but is determined based on the output that takes both into account. Become. The proportional-integral calculation section 11 only needs to be provided when the load to be protected is to be protected by the inverse time limit characteristic, and when the judgment output (output of 9) as to whether protection is necessary is large, the comparison is performed. When the protection operation output is to be obtained within a short period of time, the output of 9 is immediately introduced into the comparator 15 except for this. The second reference value generating section 13 is controlled by the output of the unbalance detecting section 23, as described above. That is, when the imbalance is large,
Since the transistor P is turned on and the reference value becomes small, the determination unit 15 uses the difference calculation unit 9
Even if the output is smaller, it will still output a signal that should be protected.

In the present invention described above, the maximum value of the outputs of the current deriving section 3 that generates a DC output proportional to each phase current is selected, and its triple value is determined by the current maximum value detecting section 21. The unbalance detector 23 calculates the subtraction of the output and the sum of each phase current. Then, the output of 23 is added together with each phase current through a diode D34 in a current adding and smoothing unit 5, and compared with the output of the first reference value generating unit 7 in a difference calculation unit 9 to protect the load.

In this configuration, the output of the unbalance detector 23 increases as the unbalance rate increases. The output of the current addition and smoothing section 5 is the sum of the currents of each phase and the output of the unbalance detection section 23 added together. The output of the first reference value generation section 7 and the output of the current addition and smoothing section 5 are compared, and if the output of the current addition and smoothing section 5 is larger, the unbalanced relay provides an operating output. Therefore, the operating current changes depending on the magnitude of the unbalance factor. On the other hand, the amplification factor of the unbalance detector 23 is determined so that the unbalance rate is 100%, that is, the unbalance detecting section 23 operates at a value of 40 to 60% of the operating current value at the time of equilibrium when the first phase is the next phase.

As a result, when the total value of each phase current is the same as when balanced, the operating characteristics are the same as when they are balanced below approximately 5 to 15%, and as the unbalance rate increases sequentially, each phase operates accordingly. The total value of current also decreases,
When the unbalance rate is 100%, the total value of each phase current operates at approximately 40 to 60% of the balanced setting amount, and the local heating of the load due to unbalance is compensated for, and the total heat generation amount of the load is smaller than the balanced setting amount. operates to safely protect the load,
If it is less than that, it becomes possible to make full use of the load capacity. That is, according to the present invention, even in the case of equilibrium, slight unbalance, and extremely large unbalance,
When the load is below the withstand capacity, it fully demonstrates its capacity, and when the withstand capacity is exceeded, it has the effect of safely and reliably protecting the load.

Note that the load capacity here means: a. If the unbalance rate is as small as 5 to 10%, there is no problem in operating at the rated load, and b. Even if the unbalance rate is 100%, the load can be operated at several tens of percent. There is no problem.

This is what I said.

〔Effect of the invention〕

As described above, according to the present invention, the unbalance of each phase current is not handled simply by unbalance, but is handled relative to the magnitude of each phase current. Able to reasonably determine whether protection is necessary.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Feeder, 2... Load, 3... Current derivation part, 5... Current addition smoothing part, 7... First reference value generation part, 9... Difference calculation part, 11... Proportional integral calculation part, 13... Second reference value generation section, 15... Comparison section, 17... Output section, 19... Power supply section, 21...
Maximum current value detection section, 23...Unbalance detection section.

Claims (1)

[Scope of Claims] 1. A current derivation unit that detects each phase current supplied to a three-phase load and generates a DC output corresponding to the current, and selects the maximum value among the outputs of the current derivation unit. A maximum current detection section that outputs the triple value, an unbalance detection section that subtracts the sum of the phase currents obtained in the current derivation section from the output of the maximum current detection section, and an unbalance detection section that obtains the value via a diode. Compares the output of the first reference value generation section with the output of the current addition and smoothing section, and outputs when the output of the current addition and smoothing section is larger than the first reference value. An unbalanced relay consisting of a difference calculating section. 2. In the unbalanced relay described in paragraph 1, the maximum current value detection section that selects the maximum value among the outputs of the current derivation section and outputs its triple value is connected to the current derivation section of each phase via the input resistance. an operational amplifier that obtains an output, a capacitor and a first diode each provided in parallel with the operational amplifier, a second diode provided on the output side of the operational amplifier, and a second diode connected in parallel with the series circuit of the operational amplifier. The conduction direction of the first and second diodes is set to the input terminal side of the operational amplifier, and the connection point of the second diode and the resistor is commonly connected. An unbalanced relay characterized by having an output terminal. 3 A current derivation unit that detects each phase current supplied to the three-phase load and generates a DC output corresponding to this, selects the maximum value among the outputs of the current derivation unit, and outputs the tripled value. An unbalance detection section that subtracts the sum of the currents for each phase obtained in the current derivation section from the output of the maximum current value detection section, an output of the unbalance detection section obtained via the diode and each phase a current addition and smoothing unit that adds current; a difference calculation unit that compares the output of the first reference value generation unit with the output of the current addition and smoothing unit and outputs an output when the output of the current addition and smoothing unit is larger than the first reference value; An unbalanced relay comprising: an integrating circuit that integrates the output of the difference calculating section; and an output circuit that outputs when the output of the integrating circuit or the output of the unbalance detecting section reaches a predetermined value.