GB2095058A

GB2095058A - Voltage supplies or relays

Info

Publication number: GB2095058A
Application number: GB8206989A
Authority: GB
Original assignee: Hartmann and Braun AG
Current assignee: ABB Training Center GmbH and Co KG
Priority date: 1981-03-12
Filing date: 1982-03-10
Publication date: 1982-09-22
Also published as: CH653479A5; DE3109330A1; SE446919B; SE8201150L

Abstract

A circuit arrangement for feeding an overcurrent time lag relay 7 has one current converter 2, 3 per phase protected, and the measurement signal and the auxiliary voltage for supply of the relay are both derived from the converter via a rectifier bridge 4. The latter supplies a Zener diode 8 in series with a resistor 9, and the auxiliary voltage is taken off across the Zener diode. <IMAGE>

Description

SPECIFICATION A circuit arrangement for feed of overcurrent time lag relays The invention relates to a circuit arrangement for feed of overcurrent time lag relays having one current converter per phase, both the measurement signal and the auxiliary voltage required for its operation being derived from the said converter via a rectifier bridge.

The formation about the alternating current, which is required for measurement, is supplied to the overcurrent time lag relays which are used in a.c. mains to monitor short circuits. The auxiliary voltage of the electronic measurement unit is frequently taken from a d.c. battery provided within the system.

In many sub-stations however, there is no d.c.

battery. In such cases the information regarding the level of current, which is required for monitoring, and the auxiliary voltage required for the electronic measurement unit have to be derived from the converter current.

A circuit arrangement of this type is known from German Offenlegungsschrift No. 2,427,621.

The circuit arrangement described there for feeding electronic safety relays has one converter and one rectifier circuit per phase, the output d.c.

voltage being supplied via a voltage controller and a precision stabilizer to a load. If the circuit is so designed that it takes over any short circuit current which may arise using measurement techniques, then the currents which are to be measured may be so low during normal operation that the secondary power of the converter is no longer sufficient to feed the circuit. In order to remedy this an additional mains feed device is proposed and its current is introduced into the circuit via a diode.

In German Auslegeschrift No. 1,961,686 an overcurrent safety relay is proposed which is able to operate with only one current converter per phase and derives the measurement signal and the auxiliary voltage from this current converter.

in this case the positive halfwave is used for the auxiliary voltage and the negative halfwave is used for the measurement signal. This separation is necessary because the current required for the auxiliary voltage changes depending on the condition of the electronic measurement unit and therefore the distribution of current between the current of the measuring circuit and the current of the Zener diode limiting the auxiliary voltage varies. Delays in charging up the relatively large storage capacitor by means of the auxiliary voltage may have a disadvantageous effect if, when the line to be monitored is switched on, there is already a short circuit because charging only takes place during every other current halfwave.

A further problem is that the different loading in both half waves leads to initial d.c.

magnetization of the converters which falsifies the vaiues.

The object underlying the invention is to link precise detection of the measurement values with secure voltage supply to the measurement circuit at the lowest possible circuit cost.

Accordingly, the invention provides a circuit arrangement for feed of overcurrent time lag relays having one current converter per phase, both the measurement signal and the auxiliary voltage required for supply being derived from the said converter via a rectifier bridge, wherein a Zener diode is connected in series with a measurement resistor to the output terminals of the rectifier bridge and the auxiliary voltage of the measurement circuit is tapped off the Zener diode.

Two exemplary embodiments of the invention will now be described with reference to the drawings, in which: Fig. 1 shows a single phase measuring circuit, and Fig. 2 shows a three phase measuring circuit.

In Fig. 1 the input current converter 3 of the safety relay is supplied by the line 1 via a main current converter 2, said converter 3 supplying a rectifier bridge 4, a diode 5 and a smoothing capacitor 6. The auxiliary voltage UH for the electronic measurement unit 7, which is shown boxed in chain lines, is tapped off at this capacitor. A Zener diode 8 limits the auxiliary voltage UH. The sum of the currents of the Zener diodes 8 and of the electronic measurement unit 7 is supplied to the current converter 3 via a measurement resistor 9 and the bridge rectifier 4.

The measured signal is supplied to the input of the measuring circuit 7 via a high resistance voltage divider 10, 11 from the measurement resistor 9. An input comparator 12 in the measuring circuit 7 compares the negative halfwaves of the measurement resistor 9 with the zero potential of the auxiliary voltage, said negative halfwaves having been raised by means of resistors 10, 11. If the voltage between the resistors 10 and 11 is negative then the comparator 1 2 switches over an output comparator 1 9 via the pulse expansion element (1 5, 16, 17, 18). The said output comparator 19 controls an auxiliary relay 20 which causes the protected line 1 to be switched off.

Fig. 2 shows the general principle of the three phase embodiment of the circuit with phase lines L1, L2, L3. The only difference is the rectifier circuit used. In this case a three-phase current rectifier bridge 21 with a star point is connected to the input current converters 22, 23, 24. The maximum peak value of the voltage across resistor 9 corresponds to the peak value of the iargest current and is evaluated as described in Fig. 1.

The general principle described is particularly simple, precise and reliable.

Claims

1. A circuit arrangement for feed of overcurrent time lag relays having one current converter per phase, both the measurement signal and the auxiliary voltage required for supply being derived

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A circuit arrangement for feed of overcurrent time lag relays The invention relates to a circuit arrangement for feed of overcurrent time lag relays having one current converter per phase, both the measurement signal and the auxiliary voltage required for its operation being derived from the said converter via a rectifier bridge. The formation about the alternating current, which is required for measurement, is supplied to the overcurrent time lag relays which are used in a.c. mains to monitor short circuits. The auxiliary voltage of the electronic measurement unit is frequently taken from a d.c. battery provided within the system. In many sub-stations however, there is no d.c. battery. In such cases the information regarding the level of current, which is required for monitoring, and the auxiliary voltage required for the electronic measurement unit have to be derived from the converter current. A circuit arrangement of this type is known from German Offenlegungsschrift No. 2,427,621. The circuit arrangement described there for feeding electronic safety relays has one converter and one rectifier circuit per phase, the output d.c. voltage being supplied via a voltage controller and a precision stabilizer to a load. If the circuit is so designed that it takes over any short circuit current which may arise using measurement techniques, then the currents which are to be measured may be so low during normal operation that the secondary power of the converter is no longer sufficient to feed the circuit. In order to remedy this an additional mains feed device is proposed and its current is introduced into the circuit via a diode. In German Auslegeschrift No. 1,961,686 an overcurrent safety relay is proposed which is able to operate with only one current converter per phase and derives the measurement signal and the auxiliary voltage from this current converter. in this case the positive halfwave is used for the auxiliary voltage and the negative halfwave is used for the measurement signal. This separation is necessary because the current required for the auxiliary voltage changes depending on the condition of the electronic measurement unit and therefore the distribution of current between the current of the measuring circuit and the current of the Zener diode limiting the auxiliary voltage varies. Delays in charging up the relatively large storage capacitor by means of the auxiliary voltage may have a disadvantageous effect if, when the line to be monitored is switched on, there is already a short circuit because charging only takes place during every other current halfwave. A further problem is that the different loading in both half waves leads to initial d.c. magnetization of the converters which falsifies the vaiues. The object underlying the invention is to link precise detection of the measurement values with secure voltage supply to the measurement circuit at the lowest possible circuit cost. Accordingly, the invention provides a circuit arrangement for feed of overcurrent time lag relays having one current converter per phase, both the measurement signal and the auxiliary voltage required for supply being derived from the said converter via a rectifier bridge, wherein a Zener diode is connected in series with a measurement resistor to the output terminals of the rectifier bridge and the auxiliary voltage of the measurement circuit is tapped off the Zener diode. Two exemplary embodiments of the invention will now be described with reference to the drawings, in which: Fig. 1 shows a single phase measuring circuit, and Fig. 2 shows a three phase measuring circuit. In Fig. 1 the input current converter 3 of the safety relay is supplied by the line 1 via a main current converter 2, said converter 3 supplying a rectifier bridge 4, a diode 5 and a smoothing capacitor 6. The auxiliary voltage UH for the electronic measurement unit 7, which is shown boxed in chain lines, is tapped off at this capacitor. A Zener diode 8 limits the auxiliary voltage UH. The sum of the currents of the Zener diodes 8 and of the electronic measurement unit 7 is supplied to the current converter 3 via a measurement resistor 9 and the bridge rectifier 4. The measured signal is supplied to the input of the measuring circuit 7 via a high resistance voltage divider 10, 11 from the measurement resistor 9. An input comparator 12 in the measuring circuit 7 compares the negative halfwaves of the measurement resistor 9 with the zero potential of the auxiliary voltage, said negative halfwaves having been raised by means of resistors 10, 11. If the voltage between the resistors 10 and 11 is negative then the comparator 1 2 switches over an output comparator 1 9 via the pulse expansion element (1 5, 16, 17, 18). The said output comparator 19 controls an auxiliary relay 20 which causes the protected line 1 to be switched off. Fig. 2 shows the general principle of the three phase embodiment of the circuit with phase lines L1, L2, L3. The only difference is the rectifier circuit used. In this case a three-phase current rectifier bridge 21 with a star point is connected to the input current converters 22, 23, 24. The maximum peak value of the voltage across resistor 9 corresponds to the peak value of the iargest current and is evaluated as described in Fig. 1. The general principle described is particularly simple, precise and reliable. Claims

1. A circuit arrangement for feed of overcurrent time lag relays having one current converter per phase, both the measurement signal and the auxiliary voltage required for supply being derived from the said converter via a rectifier bridge, wherein a Zener diode is connected in series with a measurement resistor to the output terminals of the rectifier bridge and the auxiliary voltage of the measurement circuit is tapped off the Zener diode.

2. A circuit arrangement according to Claim 1 wherein a high resistance voltage divider is also connected to the output terminals of the rectifier bridge and its output modulates an input comparator of the measurement circuit.

3. A circuit arrangement according to Claims 1 and 2 for a three phase network, wherein a three phase rectifier bridge with a star point is connected after the input current converters.

4. A circuit arrangement substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.