GB1604493A - Apparatus for continuously monitoring earth leakage current - Google Patents

Description

(54) APPARATUS FOR CONTINUOUSLY MONITORING EARTH LEAKAGE CURRENT (71) We, REDSURE ELECTRICAL LIM ITED, a British Company of Turner Street, Denton, Manchester, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to apparatus for continuously monitoring the earth leakage current flowing in the electrical supply of a piece of electrical equipment.

It is common practice, particularly in large electrical installations such as are to be found in hospitals and department stores, to incorporate in the supply to that store or hospital an earth leakage circuit breaker which will automatically trip out in the event that the earth leakage current exceeds a certain predetermined value. When this occurs, it is necessary for an electrician to individually check all of the circuits in the installation to determine the origin of the fault. This is both time consuming and expensive and, of course, whilst it is being done the installation as a whole receives no power.

According to the present invention, there is provided apparatus for continuously monitoring the earth leakage current flowing in the supply to a piece of AC electrical equipment comprising an earth leakage circuit breaker adapted to be connected in the supply line, first detector means adapted to be connected to the supply line downstream of the circuit breaker, an alarm connected to the first detector means operative to actuate in the event of an earth leakage fault, second detector means comprising a current transformer adapted to be connected to the supply downstream of the circuit breaker and a meter connected to the current transformer adapted to monitor out of balance currents flowing in the supply line.

The meter employed may be either analogue or digital. Advantageously, the signal received from the current transformer is amplified before being fed to the meter. In a preferred embodiment, the earth leakage circuit breaker is operative to switch off the supply to the piece of electrical equipment in the event of the earth leakage current exceeding a certain predetermined amount. If desired, an alarm circuit having both visual and audible elements can be associated with the circuit breaker to indicate that a fault condition has been sensed.

The invention also comprises an installation incorporating apparatus of the type defined above.

In order that the invention may be more clearly understood, two embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the circuit diagram of one form of earth leakage detection and monitoring unit.

Figure 2 shows the circuit diagram of another form of earth leakage detection and monitoring unit, and Figure 3 shows a precision amplifier/rectifier forming a part of each of the embodiment of Figures 1 and 2.

Referring to Figure 1, a single phase alternating current supply 1 is shown supplying a load 2. The supply to the load passes through an earth leakage circuit breaker comprising a double pole switch 3 and a combined balanced core current transformer 4 and relay 5. The current transformer is operative to sense any earth leakage current flowing and to energise the relay 5 when a predetermined earth linkage current is sensed. A further relay coil 6 is used to detect the disconnection of the supply by the earth leakage circuit breaker in the event of an excessive earth leakage current flowing and the relay contacts 7 are disposed in the supply circuit of a visual and audible alarm indicated by the general reference numeral 8.

The alarm comprises warning lamps 9 and 10 and an oscillator and a loudspeaker 11. Both lamps and speaker are fed from the secondary side of a transformer 12, the primary 13 of which is fused at 14 and is connected between the live and neutral conductors of the supply. The secondary output is rectified by means of a full wave diode bridge rectifier 15.

A further current transformer 16 is associ ated with the supply and is combined with a precision amplifier/rectifier 17 which feeds a precision meter 18. This circuit provides a continuous monitoring function to supplement the alarm circuitry described above as the meter will give a continuous readout of any earth leakage current flowing in the supply. When an earth leakage fault occurs which is considered to be dangerous the meter 18 will indicate a danger level reading and the relay 5 will be energised through the current transformer 4. This energisation of the relay 5 will trip the earth leakage circuit breaker. In addition, as coil 6 thereby energised relay contacts 7 will move to a position in which the circuit to lamp 10 is completed and lamp 10 illuminated indicating that the earth leakage circuit breaker has tripped out and a fault exists.The circuit to the speaker 11 of the audible alarm is completed at the same time although this alarm may be muted by opening a switch 19.

The earth leakage circuit breaker comprises an integral test circuit consisting of a push button 20 and resistor 21. When the button 20 is pushed the live and neutral of the supply are bridged via a resistor and the circuit breaker should trip out it if is working correctly as an out of balance current will then flow in the neutral.

The circuit arrangement shown in Figure 2 is more or less the same as that of Figure 1, but for a three-phase supply 30 supplying a load 31 through a three-phase earth leakage circuit breaker comprising a balanced core current transformer 32 having windings associated with each of the three phases and the neutral, a relay 33 and a four pole switch 34.

A further relay comprises a relay coil 35 and relay contacts 36 set to close a circuit from the secondary winding 37 of a transformer 38 the primary winding 41 of which is connected across two phases of the supply, to one of two lamps 39 and 40 indicating a fault or no fault condition as the case may be. The earth leakage circuit breaker has a test circuit as before comprising a push button 42 and resistor 43, operation of the push button 42 short circuiting two phases of the supply via a resistor to trip the circuit breaker if it is functioning correctly.

A monitoring arrangement comprising a further balanced core current transformer 45, amplifier rectifier 46 and meter 47 is provided to continuously monitor the earth fault leakage current flowing.

Referring to Figure 3, the amplifier/rectifier arrangement (17 in Figure 1 and 46 in Figure 2) comprises three operational amplifiers 50, 51 and 52 the first of which effectively receives across its two inputs 53 and 54 a potential representing the earth leakage current on the balanced core current transformer detected by the detection coil 55 forming part of the earth leakage circuit breaker. This potential is amplified by the amplifier and fed to the meter (18 in Figure 1, 47 in Figure 2). The arrangement may be calibrated and zero adjusted using the variable resistors 56 and 57.

In the above described embodiments, an incipient fault condition can be detected some time before an alarm level is reached.

Furthermore, because of the individual nature of the monitoring to each piece of equipment, it is a fairly simple exercise to determine which piece of equipment is producing the fault. If desired, and this is particularly advantageous where there are a large number of different pieces of electrical equipment to be monitored, the meters may be located in a bank at a remote location.

Similarly, the warning lamps and audible alarm may be similarly located, the tappings in this case being taken from the points marked "X" in the drawings of Figures 1 and 2.

WHAT WE CLAIM IS: 1. Apparatus for continuously monitoring the earth leakage current flowing in the supply to a piece of AC electrical equipment comprising an earth leakage circuit breaker adapted to be connected in the supply line, first detector means adapted to be connected to the supply line downstream of the circuit breaker, an alarm connected to the first detector means operative to actuate in the event of an earth leakage fault, second detector means comprising a current transformer adapted to be connected to the supply downstream of the circuit breaker and a meter connected to the current transformer adapted to monitor out of balance currents flowing in the supply line.

2. Apparatus as claimed in Claim 1, in which the meter is an analogue meter.

3. Apparatus as claimed in Claim 1, in which the meter is a digital meter.

4. Apparatus as claimed in Claim 1, 2 or 3, in which an amplifier is disposed between the current transformer and the meter.

5. Apparatus as claimed in any preceding claim, wherein the earth leakage circuit breaker comprises a current transformer and a relay, the current transformer being operative to actuate the relay when a predetermined earth leakage current is sensed to cause the circuit breaker to break to isolate the piece of electrical equipment from the supply.

6. Apparatus as claimed in Claim 5, in which the first detector means comprises a further relay having a coil and a set of contacts associated with the earth leakage circuit breaker, the contacts being disposed in the circuit of the alarm such that, when the relay operates, the alarm is activated.

7. Apparatus as claimed in Claim 6, in

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

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. ated with the supply and is combined with a precision amplifier/rectifier 17 which feeds a precision meter 18. This circuit provides a continuous monitoring function to supplement the alarm circuitry described above as the meter will give a continuous readout of any earth leakage current flowing in the supply. When an earth leakage fault occurs which is considered to be dangerous the meter 18 will indicate a danger level reading and the relay 5 will be energised through the current transformer 4. This energisation of the relay 5 will trip the earth leakage circuit breaker. In addition, as coil 6 thereby energised relay contacts 7 will move to a position in which the circuit to lamp 10 is completed and lamp 10 illuminated indicating that the earth leakage circuit breaker has tripped out and a fault exists.The circuit to the speaker 11 of the audible alarm is completed at the same time although this alarm may be muted by opening a switch 19. The earth leakage circuit breaker comprises an integral test circuit consisting of a push button 20 and resistor 21. When the button 20 is pushed the live and neutral of the supply are bridged via a resistor and the circuit breaker should trip out it if is working correctly as an out of balance current will then flow in the neutral. The circuit arrangement shown in Figure 2 is more or less the same as that of Figure 1, but for a three-phase supply 30 supplying a load 31 through a three-phase earth leakage circuit breaker comprising a balanced core current transformer 32 having windings associated with each of the three phases and the neutral, a relay 33 and a four pole switch 34. A further relay comprises a relay coil 35 and relay contacts 36 set to close a circuit from the secondary winding 37 of a transformer 38 the primary winding 41 of which is connected across two phases of the supply, to one of two lamps 39 and 40 indicating a fault or no fault condition as the case may be. The earth leakage circuit breaker has a test circuit as before comprising a push button 42 and resistor 43, operation of the push button 42 short circuiting two phases of the supply via a resistor to trip the circuit breaker if it is functioning correctly. A monitoring arrangement comprising a further balanced core current transformer 45, amplifier rectifier 46 and meter 47 is provided to continuously monitor the earth fault leakage current flowing. Referring to Figure 3, the amplifier/rectifier arrangement (17 in Figure 1 and 46 in Figure 2) comprises three operational amplifiers 50, 51 and 52 the first of which effectively receives across its two inputs 53 and 54 a potential representing the earth leakage current on the balanced core current transformer detected by the detection coil 55 forming part of the earth leakage circuit breaker. This potential is amplified by the amplifier and fed to the meter (18 in Figure 1, 47 in Figure 2). The arrangement may be calibrated and zero adjusted using the variable resistors 56 and 57. In the above described embodiments, an incipient fault condition can be detected some time before an alarm level is reached. Furthermore, because of the individual nature of the monitoring to each piece of equipment, it is a fairly simple exercise to determine which piece of equipment is producing the fault. If desired, and this is particularly advantageous where there are a large number of different pieces of electrical equipment to be monitored, the meters may be located in a bank at a remote location. Similarly, the warning lamps and audible alarm may be similarly located, the tappings in this case being taken from the points marked "X" in the drawings of Figures 1 and 2. WHAT WE CLAIM IS:

1. Apparatus for continuously monitoring the earth leakage current flowing in the supply to a piece of AC electrical equipment comprising an earth leakage circuit breaker adapted to be connected in the supply line, first detector means adapted to be connected to the supply line downstream of the circuit breaker, an alarm connected to the first detector means operative to actuate in the event of an earth leakage fault, second detector means comprising a current transformer adapted to be connected to the supply downstream of the circuit breaker and a meter connected to the current transformer adapted to monitor out of balance currents flowing in the supply line.

2. Apparatus as claimed in Claim 1, in which the meter is an analogue meter.

3. Apparatus as claimed in Claim 1, in which the meter is a digital meter.

4. Apparatus as claimed in Claim 1, 2 or 3, in which an amplifier is disposed between the current transformer and the meter.

5. Apparatus as claimed in any preceding claim, wherein the earth leakage circuit breaker comprises a current transformer and a relay, the current transformer being operative to actuate the relay when a predetermined earth leakage current is sensed to cause the circuit breaker to break to isolate the piece of electrical equipment from the supply.

6. Apparatus as claimed in Claim 5, in which the first detector means comprises a further relay having a coil and a set of contacts associated with the earth leakage circuit breaker, the contacts being disposed in the circuit of the alarm such that, when the relay operates, the alarm is activated.

7. Apparatus as claimed in Claim 6, in

which the alarm circuit comprises two warning lamps one indicating that the relay has been energised and the other that the relay is unenergised and an audible alarm.

8. Apparatus for continuously monitoring the earth leakage current flowing in the supply to a piece of AC electrical equipment substantially as hereinbefore described with reference to Figures 1 and 3 or to Figures 2 and 3 of the accompanying drawings.

9. An installation comprising a power supply and one or more pieces of AC electrical equipment adapted to be fed from the power supply and apparatus as claimed in any one of the preceding claims disposed in the power supply for the or each piece of electrical equipment.