AU605386B2 - Polarity testing device - Google Patents

Description

1 605386 amending ~s pi-inti:;g COMMONWEALTH OF AUSTRALIA The Patents Act 1952-1969 Name of Applicant: Address of Applicant: a *9 0e9 9 9009 9,9.

99 90* 09 9 Gag a 9 9 9 9* Actual Inventors: THE SOUTH EAST QUEENSLAND ELECTRICITY BOARD 150 CHARLOTTE STREET, BRISBANE, 4000 QUEENSLAND, AUSTRALIA RONALD JAMES COOMER and BARRY VIVIAN COX G.R. CULLEN COMPANY, Patent Trade Mark Attorneys, Dalgety House, 79 Eagle Street, Brisbane, Qld. 4000, Australia.

.ddzess for Service: '89 0 0* 9 9* 0 9 *04099 9 08*9 0 9 9 9 9 9 *9 494990 COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: POLARITY TESTING DEVICE The following statement is a full description of the invention including the best method of performing it known to

IU

,4Z* HELMUT EICHBERGER.

Commonwealth of Australia.

2 THIS INVENTION relates to a line polarity tester for testing the polarity of electrical wiring from a supply to a consumer.

Typically, consumers are supplied with a single phase electrical power at 240 volts or alternatively three phase power at 415 volts. In each of these cases, the consumer's switchboard is hard wired to a distribution network by one or more active conductors and a neutral conductor. These conductors or service conductors must be connected with the proper polarity from the distribution o network to the consumer's switchboard to ensure that potentially hazardous electrical difficulties do not occur.

Thus, the consumer's wiring terminating at the switchboard assumes a particular polarity for the neutral and the or each active conductor. It is typical for the neutral conductor at the consumer switchboard to be referenced to earth or ground.

To ensure proper polarity for connecting the switchboard to the distribution network, it has been a I statutory requirement that the linesmen performing the connection carry out testing of the service line polarity e cr S: immediately prior to making the connections between those t C C lines and the switchboard. This was carried out by the :linesmen immediately prior to making the physical connections by testing for continuity in the wiring after work at the switchboard. The linesmen ideally carry out the testing and reconnection without access to the premises at which the i 1 1 1 1 1 1 1 y 1 To: The Commissioner of Patepnts' Or a Signature of Dec arant-is) AH LWY HOI EXECUTIVE ASSISTANT TO THE CHIEF ENGINEER 3 switchboard is located. Testing usually involves measuring the impedance to ground from the active and neutral conductors.

It is typically a requirement that the neutral conductor be connected to earth at the consumer's switchboard and the neutral conductor could be identified as being the one which has the lower impedance to ground. Previously, 415 volt test lamps were used to identify the distribution network neutral conductor by placing a 240 volt voltage source across the neutral conductor and each of the other e conductors of the network in turn and check for the magnitude *of the current flow. This practice is undesirable and not condoned because of its potential danger of causing electric shock within the premises associated with the switchboard.

Other types of polarity identifying devices which *.employ a much lower level of test signal have been developed.

one known polarity tester measures the inductance to ground a go from each of the two service wires in a single phase supply.

*1114' If thie inductance is low, the conductor being tested is interpreted as being the neutral conductor. If the impedance is registered as being a high inductance (typically due to a series coil of the kilowatt hour meter used to record power consumption by the consumer) or an open circuit is detected (due to an opened main switch at the switchboard), the test is interpreted as identifying an active conductor.

I 4 The type of service polarity identification device referred to above does not always work in multiple meter installations or at locations where load control receiver relays have been installed because of the effective lowering of the inductance of the circuit tested in such installations or locations.

Other polarity testing devices which measure the magnitude of the impedance between the neutral conductor and a ground or reference potential have also been developed.

With those devices, a low level DC current derived from the qtieteI 1 6 device is caused to flow in a circuit provided by the service Sconductor and ground. The ground or reference is usually obtained by a conductive spike driven into the soil adjacent the location where testing is carried out. Detection circuitry is employed to monitor the magnitude of the *i currents caused to flow between the two service conductors in .a single phase supply. The conductor which passes the larger current is interpreted as being the neutral conductor.

*ilsjI This type of polarity testing device had its drawbacks in that it required a spiked "ground" connection t ,F which was frequently a tedious exercise to achieve and would only function at locations having a ground resistance of less than 4000 ohms. These devices were also extremely sensitive and were therefore susceptible to the influence of external electromagnetic interference or noise.

It is an object of the present invention to provide a polarity testing device which at least minimises the disadvantages referred to above.

b i According to one aspect, the invention provides a polarity testing device including a probe adapted to be coupled or connected to a service conductor of a distribution supply, two conductors for electrical connection to respective installation conductors to be identified, a Aer-; ve- Fro Pro 0 a'comparator for comparing a reference voltaget with another voltage, said another voltage consisting of the sum of the reference voltage and a voltage indicative of the resistance of one said installation conductor and indicating means responsive to an output from the comparator to provide an 0 a °9 output in use to indicate which of said installation See conductors is a neutral conductor.

ePreferably, the reference voltage is obtained from a reference resistor.

Preferably, the reference resistor is of similar magnitude to the resistance of the neutral conductor of the installation. The two voltages may be supplied directly to the comparator. However, it is preferred that both of these l voltages be supplied to the comparator via separate amplifiers. It is preferred that the amplifier interposed e between the reference voltage and the comparator have an adjustable gain to balance out the resistance of the neutral conductor.

The comparator and amplifiers referred to above may all consist of integrated circuit operational amplifiers but this is not essential.

-4-

E

-I i- The indicating means preferably provides an audible output whenever the reference voltage is less than the voltage indicative of the resistance represented by the active conductor. If desired, the indication need not be audible and may be a visual one. Where the indication is an audible one, it is preferred that a speaker or piezoelectric transducer be employed. In a particular preferred embodiment, a piezoelectric transducer is used. This transducer may be placed in the collector emitter path of a .0 bipolar transistor. The output derived from the comparator may be employed to bias the transistor into conduction to thereby ensure that the transducer provides an audible output.

ttIi tt, i I 1 t

I

R;

C.

t t II I ri LCC C C C I C t It is preferred that the testing device of the r invention includes a delay circuit which ensures that an output cannot be obtained from the comparator until a predetermined period has elapsed since the probe was coupled or connected to the service conductor. This ensures that the device does not provide spurious audible outputs in response 20 to transience which may occur during the initial stages of coupling the probe to the service conductor. In one embodiment, the delay circuit causes the voltage from the other of the installation conductors to be swamped for a predetermined time period such that the comparator is ineffective for a predetermined period of time. Preferably, the delay circuit includes a capacitor coupled between the relevant input to the comparator and a reference potential and is arranged to be charged to a predetermined level by a

I

I1 7 charging circuit. The capacitor is arranged to discharge through the separate amplifier which may be interposed between the comparator and the relevant installation conductor.

It is preferred that the comparator be a differential amplifier although this is not necessary.

A particular preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram of a polarity testing device according to an embodiment of the invention; Figure 2 is a detailed circuit diagram of the t t device shown in Figure 1; and, t T Figure 3 is a schematic drawing useful in t t describing the way in which the device of the invention operates.

With reference to Figure 1, there is shown a block C tS diagram of the device 10 according to the invention. As B shown in the figure, the meter M load, resistance RL, neutral cr resistance RN, neutral link. N/L and earth resistance RE are e C C terminated at two terminals representative of the active and neutral conductors at the consumer installation. The device of the invention has a probe P which may be coupled to a service conductor of a distribution supply. When the probe P is coupled to an active conductor of that supply, a positive voltage supply V+ is obtained from that active conductor to supply power to the device 10 via the installation earth return multiple earth neutral (MEN) to the system. This v i supply voltage V+ is obtained from the alternating voltage from the distribution supply. This voltage is halfwave rectified by diode D1 and stepped down to a suitable level by resistor Ri. Zener diode D2 together with filter capacitor Cl provide a reasonably constant source of supply V+ for the device.

The anode of zener diode D2 is coupled to a reference potential or ground. Reference resistor R is connected in series with zener diode D2 and terminates in a test terminal which in this case is colour coded and c represents a black test lead. It is from this test lead that t a reference voltage VR is obtained and supplied to amplifier 1. This amplifier has a feedback resistor RV which may be t t ,t r altered to vary the gain of the amplifier to provide an output voltage VI. This output voltage is made available as r, t one input to differential amplifier 2. The output from t t amplifier 1 is made available, via diode D3, to a low pass filter comprising resistor R5 and capacitor C4. The output Sfrom the low pass filter is coupled to input bias resistor R9 of amplifier 2. Amplifier 3 has as one of its inputs a test lead identified as the red test lead which may be coupled to one of the service conductors at the consumer installation.

The signal derived by the red test lead is supplied to amplifier 3 which has a feedback resistor R2. The output V3 obtained from amplifier 3 is supplied to amplifier 2 via input bias resistor R10. Whenever voltage VI exceeds voltage V3, amplifier 2 provides an output which is coupled to the base electrode of transistor TR1 via resistor R12. This i! 9 output turns transistor TR1 on and completes a circuit for transducer S and load resistor R13 to provide an audible output.

Amplifier 4 and its associated components ensure that when the probe P is first connected to an active service conductor, capacitor C5 is charged up to the voltage V+.

This ensures that the amplifier 2 does not provide an output.

Capacitor C5 may discharge through feedback resistor R2 and after a predetermined time set by the time constant of C5 and R2, the device may then function and the output of amplifier 2 is not inhibited.

I *Capacitor C6 and resistor R18 function as a differentiator to thereby pulse charge capacitor C5. The a time constant chosen by the values of R2 and C5 may provide for a 4 second delay before which amplifier 2 may function.

A detailed circuit diagram of the device shown in a block diagram form in Figure 1 is shown in Figure 2. In Figure 2, like annotation for the various components is used c to that edopted for the description in relation to Figure 1 except that amplifiers 1 to 4 are now identified as integrated circuits ID, 1A, 1C and 1B respectively. These amplifiers may all be provided by one integrated circuit chip. As shown in Figure 2, the input supplied to amplifier 1C is clamped or limited by reverse connected diodes D4 and D5. Circuitry consisting of series connected diode D8 and resistors R20, R21 coupled between the probe and the red lead or clip function to eliminate spurious test results in the case of a poor connection between the red lead and the i t 1 1 chosen installation conductor. Typically R20, R21 are both high resistances approximately 10 m ohm each and are swamped out by RN when a good connection is achieved.

In Figure 3, a schematic drawing of a typical consumer installation is shown. The consumer's premises are indicated by the numeral 30. The earth connection from the neutral link N/L is shown schematically by the letter E. The wiring to the consumer's switchboard is carried out and terminated in an active and a neutral conductor indicated by the letters A and N. Adjacent the consumer's premises a distribution supply consisting of 3 active conductors 31, 32 t"t and 33 as well as a neutral conductor 34 are shown. Whilst t t these conductors are shown as being supported by a utility t pole 35, it should be appreciated that the device of the invention may also be used where the supply is provided underground. The device 10 of the invention is shown with the probe P hooked over the neutral conductor. A volt meter M in series with resistor R20 is coupled across D1 and RR.

S The operation of the device 10 of the invention will now be described with reference to the figures. Once Cr f the wiring in premises 30 have been completed or is ready for reconnection to the distribution supply, the device of the invention is electrically coupled to a selected one of lines 31 to 34. Should the probe be coupled to conductor 34 the device 10 will not produce an audible output since power for it cannot be derived from the neutral conductor. The black and red test leads are electrically coupled to respective i I 1 ones of the service conductors A and N. With the probe P coupled to one of conductors 31 to 33 a DC voltage V+ is provided to power the device 10. This connection also provides a reference voltage VR to the device and also a voltage VM (see Figure The voltage generated across resistor RR and resistor RN enables amplifiers 1 and 3 to provide voltages VI and V3 respectively at their outputs. By adjusting resistor RV the voltages VI and V3 may be made equal when resistor RN equals 0.33 ohm. If, after such an adjustment (set at time of calibration and/or manufacture of the device) RN is greater than 0.33 ohm then the voltage V3 t t t t is greater than V1.

t Amplifier 2 is used in a differential mode to bias transistor TR1 on for this condition which in turn activates transducer S. Amplifier 4 is used to pulse charge capacitor 2 at the time of connection of the probe P. With capacitor C2 charged amplifier 4 is biased off. Capacitor C2 discharges through resistor R3 until the voltage V3 falls sufficiently to cause differential amplifier 2 to operate.

Amplifier 4 and its associated circuitry biases the e rr transducer S off for the time of the discharge portion of the cycle.

The device when used to test polarity operates as

-I

follows:- With no power supplied on any of the active lines of the distribution supply, no sound is emitted regardless of how the test leads are connected to the consumer installation and of the position of the probe relative to the active lines of the supply.

I

A

12 With mains energised and the test leads correctly coupled, (black lead to the neutral terminal and red lead to the active terminal of the installation), sound will be emitted when the probe is coupled to any of the active lines and of course no sound will be emitted when the probe is coupled to the neutral line of the supply.

With the test leads incorrectly connected to the installation (that is, the installation neutra. and active terminals are incorrectly identified), no sound will be 1dO emitted when the probe is coupled to any of the active lines ettirtof the supply.

I As an added feature a changeover switch may be interposed between the test leads and the connection to the t 1 4 neutral and active terminals at the installation. With such a switch, present the test procedure may readily include testing with the terminals correctly and incorrectly coupled to the test leads. This ensures that faulty wiring at the sinstallation can be positively identified with the device as well as enabling proper identification of the neutral terminal at the installation. This also enables self testing of the device.

The device of the invention operates with either the main switch open or closed at the consumer installation and requires only one test procedure before the consumer service conductors may be connected to the distribution supply. The device functions on all multiple earth neutral systems with installation earth resistances of up to 50 kohm and requires no earth probe or independent battery supply.

13 The device enables the integrity of the neutral at the consumer installation to be checked whilst determining proper polarity and is suitable for single phase or multi phase installations.

The device of the invention may be used as a 3 terminal device when the main switch at the consumer installation is closed. It can also be used as a 2 terminal device for measurements when the installation main switch is open or for detecting the voltage between phase conductors.

In a 3 terminal mode with the device coupled to an active conductor of the distribution supply a relatively constant 3CI current is provided to the probe of the device via the r St multiple earth neutral return. The red test lead when t t connected via the service conductor to the neutral link acts as a voltage probe to measure the resistance of the consumer installation between the black test lead and the neutral r V t: E link. If this resistance is less than 0.33 ohms, the device emits a tone after a predetermined delay.

c The 0.33 ohms has been set as a practical upper ccl ICC limit for the resistance of a good neutral conductor. Any value above this will be treated by the device as an active conductor and results in no sound output.

The test procedure requires all 4 supply conductors to be tested in turn. Provided the installation or service conductors is safe and connected with the correct polarity, ia tone will be emitted for all 3 energized supply conductors and no tone will identify the neutral conductor of the supply. The device does not emit a sound on any test if any of the above conditions are not true.

j i,: 1- i L i. i 14 In the 2 terminal mode, with the red test lead shorted to the black test lead, the device can be used to make measurements similar to a test lamp to indicate current flow. The device will emit a tone if the voltage between the 2 terminals exceeds 100 volts AC. This mode can be used when the main switch is open and inaccessible. In this mode the device can also be used between mains conductors like a test lamp to determine that all 3 phases and a neutral are present in a supply.

i C C c c r C C C t t 'Al

I

~i

Claims (11)

1. A polarity testing device including a probe adapted to be coupled or connected to a service conductor of a distribution supply, two conductors for electrical connection to respective installation conductors to be identified, a O rivek f'-m .he '6p comparator for comparing a reference voltagewith another voltage, said another voltage consisting of the sum of the reference voltage and a voltage indicative of the resistance of one said installation conductor and indicating means responsive to an output from the comparator to provide an 'output in use to indicate which of said installation conductors is a neutral conductor.

2. The device of Claim 1 including separate Samplifiers coupled between the reference voltage and the resistance indicative voltage and the comparator.

3. The device of Claim 1 or 2 wherein said indicating means provides an audible output.

4. The device of Claim 1 or 2 wherein the indicating means provides a visible output.

The device of Claim 3 wherein said indicating means comprises a speaker or piezoelectric transducer.

6. The device of any one of Claims 1 to 5 including a delay circuit which disables the comparator for a predetermined time period following coupling or connection of the probe to the service conductor. ;I~w~i-rurr-urrrr 1^ 111 -1-1 i t 16

7. The device of Claim 6 wherein said delay circuit includes a capacitor coupled to the relevant said comparator input and a reference potential, said capacitor being arranged to be charged to a predetermined level and to be discharged after said predetermined period.

8. The device of any one of Claims 1 to 7 wherein said comparator is a differential amplifier.

9. The device of any one of claims 1 to 8 including a voltmeter coupled between the probe and one of said two conductors.

10. The device of any one of claims 1 to 9 including a change over switch coupled to said two conductors.

11. A polarity testing device substantially as herein described with reference to Figures 1 and 2 of the drawings. DATED this EIGHTEENTH day of NOVEMBER 1988. THE SOUTH EAST QUEENSLAND ELECTRICITY BOARD By their Patent Attorneys, G.R. CULLEN CO. S 4 4441 4 IQ 44 *4 4 $1 *S t t at 4S 4 C 4 4 41sr 4 C