Hot Line Indicator

This invention relates to a voltage detector/indicator unit for providing an audio and/or visible indication of the voltage carried by high voltage electrical utility transmission lines and switchgear. The detector/indicator unit is mountable upon an electrically insulating pole, commonly referred to as a hot stick, for use by utility company linemen.

Portable meters suitable for measuring voltages have been widely utilized for many years. In such meters, the readout mechanism may be in the form of a digital display. Such displays offer higher resolution and imply more accuracy than it is possible to obtain when measuring the voltage on electrical utility lines. This could cause confusion of the utility company linemen. In some situations, the meter provides an audible and/or visible indication for indicating whether the voltage is above or below a predetermined value. However, it is desired to provide an indicator which can operate at several different voltage levels without requiring manual selection of a particular voltage range so that the operator can easily determine whether full line voltage or a lesser voltage is present on the power line being tested.

According to the invention, there is provided a voltage detector/indicator unit for use on electrical utility lines and switchgear which comprises a housing having a plurality of display means, such as lights, mounted thereon. A probe is mounted on the housing and is adapted to be placed in contact with an electrical utility line or switchgear for providing an input signal indicative of the voltage on the electrical utility line. The voltage detector/indicator unit includes circuitry providing a plurality of different reference voltages and a plurality of comparators each being connected for receiving the signal voltage and comparing it with one of the reference voltages. A plurality of output switches are provided and each of them is connected to one of the comparators so that each switch is actuated in response to an output from its associated comparator. Each switch in turn is coupled to one of the display means so that each of said display means can be operated when its associated switch is actuated.

FIG. 1 is a perspective view of a fragment of a hot stick having mounted thereon the voltage detector/indicator unit according to the present invention;

FIG. 2 is a central sectional view through the voltage detector/indicator unit; and

FIG. 3 is a circuit diagram for the voltage detector/indicator unit.

FIG. 4 is a block diagram of the integrated circuits A3, A4, A5 and A6.

The voltage detector/indicator unit 10, according to the present invention, is here shown as being mounted on a hot stick 11 so that the electrical company lineman can place the unit on an electrical utility line or switchgear which is located many feet above the ground. The hot stick 11 can be of any suitable type and forms no part of the present invention. An example of a suitable hot stick is disclosed in U.S. Pat. No. 4,079,978. The voltage detector/indicator unit 10 can also be used, in combination with commercially available bushing adapters for loadbreak bushings, to measure the voltage on underground equipment, such as pad mounted or underground switches and transformers.

The voltage detector/indicator unit 10 comprises a housing 13 for containing the electrical circuit elements of the unit, and a mounting structure 14.

The mounting structure 14 comprises a tubular support having an inner end 17 and an outer end 18. A universal mounting fitting 19 is provided on the inner end 17 of the support 16. The fitting 19 comprises a post 21 which is slidably received in the inner end of the tubular support 16 and is secured therein by an epoxy adhesive. A screw 22 is provided to hold the housing 13 to the tubular support 16 and to provide electrical contact between the circuit parts inside the housing 13 and the fitting 19. The screw 22 also helps to secure fitting 19 to the tubular support 16. The fitting 19 has an adaptor section 23 which is adapted to be coupled to a universal head 24 mounted on the end of the hot stick 11 in a conventional manner so that the support 16 can be disposed at a selectable angle to the longitudinal axis of the hot stick 11 and can be releasably clamped in such adjusted position.

Referring to FIG. 2, an end fitting 26 is slidably received in the outer end of the tubular support 16 and is releasably secured therein by an epoxy adhesive. A screw 27 is provided to hold the housing 13 to the tubular support 16 and to provide electrical contact between the circuit parts inside the housing 13 and the fitting 19. The screw 27 also helps to secure fitting 19 to the tubular support 16. A probe 28 has a shank 29 which is threaded into a central opening 31 in the end fitting and is releasably secured therein by a wing nut 32. The probe 28 is illustrated as being a curved probe which can be hung on the power line to be tested. It will be understood, however, that the probe 28 can be of any desired shape, such as a straight rod, or other suitable adapter for underground systems.

The housing 13 is of generally rectangular, box-like configuration and is comprised of an outer end wall 36, a base wall 38, a top wall 39 and a pair of sidewalls 41. The inner end wall of the housing 13 is defined by an end panel 42 on which are mounted an audible device 43, such as a horn or buzzer, and a plurality of visible indicators, here light-emitting diodes (LED). Referring to FIG. 1, there is a total of 17 LEDs comprised of a power indicator LED 44P, which may emit green-colored light, and four sets of LEDs 44A-44D, each set being comprised of four LEDs, which may emit red-colored light, arranged in a closely spaced group so that the light emitted therefrom will appear substantially as being one large light when viewed from a distance.

A printed circuit board 46 is mounted inside the housing 13. A battery 53 (FIG. 3) is removably mounted in a battery holder 47 for powering the electrical components of the voltage detector/indicator unit. A start switch SW1 is provided for starting operation of the unit 10.

A spacer 49 is provided between the base wall 38 of the housing 13 and the tubular support 16.

Referring to FIG. 3, the probe 28 is connected through a resistor R28 to the terminal 51 of a conductor 52 in order to provide an input AC signal to the unit 10. A input load resistor R9 is connected between the conductor 52 and ground whereby to provide a reduced voltage on conductor 52 indicative of the voltage of the power transmission line being tested. The resistor R8 and diodes D4 and D6 form a voltage limiter so that the resulting clamped signal 55 is supplied to the positive terminals of four operational amplifier sections A2A, A2B, A2C and A2D in parallel. The sections A2A, A2B, A2C and A2D are provided by an integrated circuit commonly known identified as a quad differential input operational amplifier, one typical example of which is a Motorola LM-224 series integrated circuit. Such integrated circuits can operate at supply voltages as low as 3.0 volts and with low input bias currents.

The power control circuit is powered by a battery 53. The start switch SW1 is connected between the battery plus terminal and the conductor 54 through a resistor R2. A field effect transistor (FET) Q1 is provided to connect the battery minus terminal to ground. When the start switch SW1 is closed, the gate of FET Q1 is brought up to the battery plus voltage, which charges capacitor C3 and turns on FET Q1. The high conductivity of FET Q1 with a gate-to-source voltage of over 2.5 VDC will then connect the battery minus terminal to the circuit common.

If no input voltage from probe 28 is detected, the charge on capacitor C3 will drain through resistance R1 as the gate-to-source voltage on FET Q1 falls to 2.5 VDC, the conductivity of FET Q1 will rapidly decrease and the battery minus terminal will be disconnected from circuit common. The time for this process to occur can be, for example, about eight minutes.

If an input voltage from probe 28 is detected, the output 1 will oscillate, thereby causing the charge on capacitor C3 to be continuously refreshed by the action of capacitor C4 and diodes D1 and D2. The resistor R3 bleeds the charge from capacitor C4 when oscillation of the output 1 ceases.

The circuit comprised of capacitor C5, diode D5 and resistor R10 is a power-up alert circuit to provide an indication that the detector/indicator unit is working. When the power is turned on by closing the start switch SW1, the line +V.sub.cc goes to battery plus voltage above circuit common, dragging the plus end of capacitor C5 with it. Since capacitor C5 cannot charge instantaneously through resistor R10, the negative end of capacitor C5 also goes substantially to battery plus voltage. This pulls the signal line 55 to almost battery plus voltage. In a manner to be described below, this causes a full voltage visual and audible indication, to the user, that the unit is operating. As capacitor C5 charges, the voltage forced onto the line 55 declines, eventually to zero. As it declines, the visual indication to the user changes from all four groups of LEDs to three, two, one and then none.

When capacitor C5 is fully charged, the diode coupling through diode D5 becomes invisible because it is effectively paralleled by the protection diode D4 from the 1 input line 55 to the line +V.sub.cc.

An internal voltage reference circuit is comprised of an integrated circuit Al which is effective as a precision reference diode. A suitable integrated circuit for this purpose is Motorola TL431ILP. The reference diode A1 functions as a shunt so that its anode voltage is maintained at whatever is required to maintain its reference voltage at a selected value. When the battery 53 is a 9V battery, the reference diode Al maintains a reference voltage at the point 56 of +2.5 VDC and generates 5.0 VDC in line 57. In the illustrated embodiment, the overall design is intended to work with a battery voltage range of from 10.5 VDC to less than 7.2 VDC. However, the basic accuracy of the unit is not significantly changed until the battery voltage is less than about 4 VDC, although the LEDs 44A-44D may be less bright.

The circuit comprised of diode D3, transistor Q2 and resistor R5 provides a means for sensing the battery voltage and it is used to control the power LED 44P on the panel 42. Transistor Q2 acts as a saturated switch when the battery voltage is above 6.8 VDC, while it is completely open at voltages below 6.2 VDC, thus turning off the power LED 44P. As indicated above, the device 10 will continue to work for several hours after the power LED 44P turns off because of the opening of transistor Q2, so that the user will have time to obtain another battery. It will be understood, however, that when Q1 is turned off, the circuit will also be turned off.

The reference voltage on line 57 is applied in parallel to the negative terminals of the operational amplifier sections A2A, A2B, A2C and A2D, through resistors R11, R16, R20 and R24 of different values. Resistors R12, R17, R21 and R25, also of different values, are connected between the negative terminals of the operational amplifier sections A2A, A2B, A2C and A2D and ground. Thus, the reference voltage on line 57 is divided into four reference voltages of different values which are applied to the negative terminals of the operational amplifier sections. For example, the reference voltage applied to the negative terminals can be 0.244V for section A2A, 0.854V for section A2B, 2.95V for A2C and 4.61V for A2D.

The clamped signal voltage received from line 52 through resistor R8 is compared with the reference voltage applied to the negative terminal in each of sections A2A, A2B, A2C and A2D. When the signal voltage is larger than one or more of the respective reference voltages, those sections will provide respective outputs which will be half-wave rectified by the respective diodes D7, D8, D9 and D10, and supplied to respective filter capacitors C6, C8, C9 and C10. The capacitors C6, C8, C9 and C10 are provided with bleeder resistors R13, R18, R22 and R26 to provide an appropriate turn-off delay. The resulting DC signals are supplied to integrated circuits A3, A4, A5 and A6 to turn on those circuits and thereby generate pulses.

The integrated circuits A3, A4, A5 and A6 are general purpose timing circuits capable of producing accurate time delays or oscillation. Suitable integrated circuits are Maxim ICM 7555, Motorola MC1455 and Signetics NE/SA/SE 556. The integrated circuit A3 is connected to freely oscillate, with its time constant being determined by capacitor C7 and resistor R14. For example, the frequency can be about 82 cycles per minute. The threshold terminals of the integrated circuits A4, A5 and A6 are each connected to the output terminal of the preceding stage so that their outputs alternate. The outputs of circuits A3, A4, A5 and A6 are connected through resistors R15, R17, R23 and R27, respectively, to the transistors Q3, Q4, Q5 and Q6. The transistors Q3-6 are provided to sink enough current for LED operation. The output 1 from transistor Q3 is applied to the audible device 43 and the group A LEDs, and the outputs 2, 3 and 4 are connected to the group B, C and D LEDs, respectively.

In use, the detector/indicator unit 10 is attached to an electrically insulating pole or hot stick 11 of suitable length. The start switch SW1 can then be turned on, which turns on the power to the unit 10. All the LEDs and the audio device will operate for a few seconds and then cycle off leaving only the power LED 44P lit. If no input signal is provided, the unit 10 will shut off automatically after about eight minutes. This will be indicated by turning off the power LED 44P.

When it is desired to use the unit to test the condition of a power line, the detector/indicator unit 10 is raised and moved toward the power line. As the unit 10 is moved toward the line and before contact is made, the first group A of LEDs and the audio device 43 may come on. Thus, if the power line has a voltage of more than a predetermined, for example, 600 VAC, the operational amplifier A2A and associated circuitry will supply pulses to circuit A3 which in turn will cause the audio device 43 to sound and the group A LEDs to flash. As the field gets stronger, additional groups B, C and D of the LEDs will be activated. The strongest field will be achieved when the-probe 28 is in contact with the power line. For example, a voltage of 600 VAC will cause the group A LEDs to flash, a voltage of 2,000 VAC will cause the group A and group B LEDs to flash, a voltage of 7,000 VAC will cause the group A, group B and group C LEDs to flash and a voltage of 11,000 VAC will cause the group A, group B, group C and group D of LEDs to flash. As mentioned above, successive groups flash alternately. For example, when group D is on group B will be on and groups A and C will be off, and then when group D turns off group B will turn off and groups A and C will turn on.

After the voltage measurement has been made, the detector/indicator unit 10 can be removed from the wire and it will turn off in a selected time, for example, about eight minutes.

The voltage detector/indicator unit according to the present invention provides both an audio and visual signal and verifies line conditions prior to the installation of protective grounding equipment. The device provides four banks of lights and an audio indicator to warn the operator of a voltage potential. A manual selector switch is not required because the banks of LEDs are preprogrammed to operate at four different voltages. The operator can easily determine whether full line voltage or a lesser voltage is present on the power line. The unit is designed for use only on bare conductors and on undergound equipment when the appropriate bushing adapter for a loadbreak bushing is used. It is not designed for use on shielded or fully insulated conductors.

Although a particular preferred embodiment of the invention has been described, the invention contemplates such changes or modifications therein as lie within the scope of the appended claims.