UA73195C2 - Method of overcurrent protection of electric installations - Google Patents

Abstract

The present invention relates to methods for protecting electric installation against overload, short-circuits, and phase asymmetry. The proposed method of overcurrent protection of an electric installation implies using the algorithm for measuring effective values of phase currents with storing data in an intermediate memory, the result of which is a minimal length of measurement intervals and a possibility to average the measurement results in order to exclude accidental errors. The method is distinctive by measuring effective current values with a shift by the measurement period, determining the average current values, and checking the excess of the specified short-circuit and overload current set values in each phase circuit of the mains load. Additionally, the monitoring of the phase currents is possible for the disconnection of the electric installation when the phase current terminates. The proposed method provides a possibility to enhance the speed of response and noise immunity of devices for controlling automatic circuit breakers designed for disconnecting power consumers in emergency states.

Description

Description of the invention

The invention relates to electrical engineering and concerns the protection of electrical installations against current 2 overloads, short circuits and phase distortion.

A known method of detecting damage in an alternating current network |1) is used to determine the value of the current, compare it with the permissible value and judge the presence of damage, and at the moment of the current passing through zero, the predicted amplitude value of the current is determined as the result of dividing the derivative of the current by its circular frequency.

The disadvantage of the method is that the effective value of the current is determined for a time equal to approximately a quarter of the period of the industrial frequency; and taking into account the time required to determine the derivative of the current, the signal of damage in the network can be produced no earlier than 0.05s. In addition, this method has insufficient protection against impulse interference, which leads to unreasonable disconnection of the network.

There is also a known method implemented in the electronic data processing circuit for turning off the overload current 12 (21, according to which the current is measured and its analog-to-digital conversion is carried out, the current value of the current is continuously determined during a certain time interval at equal time intervals, the obtained value is compared with the permissible current, determine the nature of the emergency mode and turn off the electrical installation. The microcontroller monitors with the help of a given time frame the number of excesses of the set value of the current over the actual value, and when this set value is repeatedly repeated, it turns off the installation.

The disadvantage of such a scheme is the lack of selection of the nature of the emergency mode: whether it is a short circuit or an overload. In addition, false alarms from short-term transient processes are not excluded.

Closest in terms of technical substance to the claimed invention is the method of instant protection in the decoupling unit |C), the electronic decoupling unit contains a microcontroller and a corresponding memory device with the program of the device, initialization parameters and loading procedure, as well as Ge) memory device with operating parameters. Algorithm - an instant protection program stored in a memory device, has a waiting state and an execution state. In the execution state, it determines the digital values of the current and stores them in the register. The accumulation of a certain number of values is perceived as the peak value of the current. Peak values are stored in a separate register. When the number in the register becomes greater than the limit o value, the program gives a signal to the microcontroller to activate the decoupling unit. Ge")

The disadvantage of this method is the lack of justification for the value of the limit number of current overshoots, which leads to the uncertainty of the amount of energy that is transferred to the consumer. With this method, the nature of exceeding the limit value of the current (short circuit, overload) is not evaluated, and the speed of operation with a short circuit is insufficient, because the time interval in the initial state is not filled.

The basis of the invention is the task of creating a method of maximum current protection of an electrical installation - in which, by introducing the principle of an updated buffer, a compromise is ensured in the measurement algorithm (the time for evaluating the effective current value is minimized and protection against instantaneous errors and disturbances is achieved due to the averaging of measurements), which leads to increasing the speed and immunity of the electronic unit. "

The problem is solved by the fact that in the method of maximum current protection of the electrical installation, in which C 70 current is measured and its analog-digital conversion is carried out, the current c value of the current is continuously determined during a certain time interval at equal time intervals, much smaller than half of the period of the controlled current , compare the obtained value with the permissible current, determine the nature of the emergency mode and turn off the electrical installation, determine the current value with a shift of the time interval by the amount of the next count, the weighted average value of the current for each interval is determined for each phase of the network and successively check the exceedance of the settings for a short 7 shorting and overloading. со Additionally, the control of the value of the operating currents can be introduced to disconnect the electrical installation when the current in the phases disappears, and the initial state of filling the measurement time interval can correspond to the nominal value of the current of the electrical installation. (Те) 20 The use of such a renewable buffer minimizes the duration of the evaluation of the current values and provides protection against instantaneous errors and interference due to the division of each measured reading by the value of the slip (averaging), which ensures an increase in the speed and immunity of the electronic unit of the automatic circuit breaker disconnection.

The method of maximum current protection of electrical installations can be traced on the example of the functioning of the 25 electronic unit, the scheme of which is given in the drawing. Here, the algorithm for controlling the current in one phase is shown; two

HF) other phases are controlled similarly.

The input signal of the electronic unit from the current transformer | enters the input of the analog-to-digital converter 2. Each subsequent count is carried out with a time interval of PO in which the number of counts t-10-100 t 60 is determined by the speed of the processor of the electronic unit (the greater the value of t, the more quickly the current value is measured, however, the restraining factor is that during the time vl, t a full cycle of processing the results must be carried out with the verification of overload, short-circuit and phase misalignment conditions with the output of signals to the executive device).

The composition of the buffer From the random access memory device (RAM) is updated at each measurement cycle and the recorded values are shifted, pushing out the oldest measurement and adding a new measurement count to the beginning of the buffer. After that, the weighted average values of the operating currents are calculated by software based on a sample of measurements of a fixed length t using the formula:

X, - i-th instantaneous value of the controlled current; t - the number of readings of the measurement sample;

K is the proportionality factor.

In order to reduce the reaction time of the electronic unit to a short circuit in the network during initial switching on, the primary state of all elements of the RAM buffer must correspond to the nominal value of the circuit breaker current.

When the value of the operating current is exceeded, the solving blocks (1-3 according to the number of phases) enter the algorithm. The organization of checking the logical conditions for exceeding the overload and short-circuit current settings involves the simultaneous start of the time counters of the overload and short-circuit current counters. In the event of a short circuit.

This provides comprehensive protection of the network against overloads, if the short-circuit tripping condition ceases to be fulfilled before the set time expires, and the overload tripping condition is maintained.

Checking the condition of instantaneous operation of the cut-off switch is carried out regardless of overload and short-circuit conditions with a time setting. This provides instant cut-off of the phases regardless of the state of the tr and ace time counters.

The fourth resolving unit monitors the values of the active currents of all 3 phases and produces a switch-off signal when a phase-break condition is met. high school

The result of the operation of the algorithm of the electronic unit in each measurement cycle is the presence or absence of a signal coming to the decoupling executive device depending on the situation accumulated in (8) in each of the three RAM buffers.

Sources of information 1. Patent of Ukraine 27421 C2, cl. НО2НЗ/О8, 2000. у зо 2. German patent 98 19851752 AIi, cl. НО2НЗ/О8, 2000. 3. US patent 6078489 A, cl. НО2НЗ/О8, 2000. - prototype. me)

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Claims (2)

The formula of the invention 1. The method of maximum current protection of electrical installations, according to which the current is measured and its analog-to-digital conversion is carried out, the current value of the current is continuously determined during the set time interval at equal time intervals, the obtained value is compared with the permissible current, the nature of the emergency mode is determined and the electrical installation is turned off, which differs in that 65 determinations of the operating value of the current are carried out with a shift of the time interval by the value of the next count, the weighted average value of the operating current for each interval is determined for each phase of the network and the exceeding of the short-circuit and overload settings is successively checked. 2. The method according to claim 1, which is distinguished by the fact that the values of the operating currents are additionally monitored for further disconnection of the electrical installation in the event of a current loss in the phases. Q. The method according to claim 1, which differs in that the initial state of filling the time interval begins to be measured at the nominal value of the current of the electrical installation. Official bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2005, M 6, 15.06.2005. State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. 6) IF) (o) «- (ze) and - - and? -i (95) - se) sl ime) 60 b5