US3007108A - Control panel system - Google Patents

Description

Oct. 31, 1961 w. c. SEALEY 3,007,108

CONTROL PANEL SYSTEM Filed Nov. 4, 1957 49 M KW United States Patent Ofifice 3,ll7,l%8 Patented Oct. 31, 1961 3,007,108 CONTROL PANEL SYSTEM William C. fiealey, Wauwatosa, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Nov. 4, 1957, Ser. No. 6%,238 4 Claims. (Cl. 324-28) This invention relates in general to a control panel for electrical regulating apparatus and more specifically to a novel means for providing an adjustable voltage for calibrating or testing the voltage sensing means of a voltage or phase angle regulator.

Voltage sensing means are frequently used for automatically controlling the switching of capacitors or transformer taps to regulate the phase angle or voltage of an electrical distribution network. The voltage sensing device and the circuit elements linking it with the motor controls of the regulator are generally referred to as the control panel. Magnetic relays which are actuated by the voltage of the regulated system are often used for this voltage sensing purpose. Relays generally have electrical or mechanical adjustments for determining the points at which the relay contacts close and for determining the band width or voltage range over which the contacts remain open. When the regulator is installed in the field, the relay is set to the desired voltage level and band width. A calibrating or testing voltage of the desired range is applied to the relay circuit and the electrical or mechanical adjustments are made until the desired relay action is obtained. Since the relay actuating voltage from the transmission line may be below the voltage required for the maximum test voltage it is necessary to provide some means for increasing this voltage. Inasmuch as the relay may be checked or reset periodically throughout its years of service it is desirable to include the voltage raising means as a part of the control panel.

One simple way of raising the voltage to the relay is to operate the regulator manually to raise the line voltage. However, this temporarily defeats the purpose of the regulator as it changes the voltage supplied to the load.

Another method of the prior art for obtaining the desired test voltage calls for a variable autotransforrner which is connected into the panel during the test. This method of obtaining a higher voltage is unsatisfactory because of the difficulty in isolating the panel and making the connections to the autotransformer. Providing a permanently connected auto transfo-rmer is also unsatisfactory because the autotransformer is expensive and requires appreciable space in the control panel cabinet.

This invention provides a simple means for raising the voltage across the voltage sensitive relay to the desired level for a test or calibration by calling for a capacitor and variable resistance which can be connected in series with the relay. It is well known that the total impedance of a circuit containing an inductance such as a magnetic relay may be lowered by introducing a capacitance in the circuit. The voltage across the inductance and the other circuit elements will be raised by the increased current. The voltage may then be adjusted to the level required for the test by means of the variable resistance. The voltage raising device of this invention is simple and inexpensive to manufacture and it provides a wide range of voltage values both above and below the available signal voltage.

Therefore, it is an object of this invention to provide a new and improved control panel for a regulating device.

Another object of this invention is to provide a new and improved means for adjusting the signal to a voltage sensitive control device to a level above or below the existing signal.

responds by signaling the regulator.

Objects and advantages will be apparent from the following description when read in connection with the accompanying drawings in which:

FIG. 1 is an impedance diagram illustrating the effects of reducing the total reactance in a circuit;

FIG. 2 is a schematic view of a regulator control panel; and

FIG. 3 is a vector diagram illustrating the voltage raising and adjusting effect of the control panel using this invention.

While numerous control circuits exist to which this invention is applicable, it may conveniently be illustrated in connection with a conventional voltage regulator control panel using a line drop compensator.

Referring to the drawing and particularly to FIG. 1 the total impedance of an electrical circuit may be varied by changing the total reactance of the circuit. Thus, a circuit containing a resistance R in series with an inductance X and no capacitance has a total impedance Z By introducing into the circuit a capacitance X which counteracts in part inductance X the total impedance of the circuit is reduced to a value Z It is apparent that where the current of a circuit having a constant voltage input equals the voltage divided by the total impedance the current Will increase upon a decrease in the impedance.

It is this principle of increasing the line current by decreasing total impedance which is embodied in applicants novel device for testing or calibrating a reactance circuit such as a voltage regulating device in a control panel of a regulator. The control panel 11 of FIG. 2 cooperates with a conventional tap changer and motor, not shown for simplicity, to regulate the voltage in a power line. Panel 11 comprises a potential circuit 12 and a current circuit 13. The potential circuit comprises a potential transformer 14, a voltage sensitive regulating relay 16, a first variable resistor 17, a variable inductance 18 and a second variable resistance 19. The current circuit includes a current transformer ll and is coupled to the potential circuit by variable inductance 18 and variable resistance 19. The combination of the current circuit and inductance 18 and resistance 19 is generally referred to in the trade as a line drop compensator. Its purpose is for raising the output voltage sufiiciently to compensate for the voltage drop from the regulator to the load center.

In operation potential transformer 14 which is connected across the output terminals of the regulator supplies a proportionately reduced voltage to voltage regulating relay 16. The voltage across relay 16 is the combination of the voltage at the regulator as measured by potential transformer 14 and the voltage drop in a portion of the transmission line as measured by current transformer 21 in combination with variable inductance 18 and variable resistance 19. Relay 16 is responsive to voltage variations with respect to a predetermined voltage band width. The desired range of voltages at which relay 16 is balanced is obtained by adjusting variable resistance 17. Thus, when the output voltage drops below its desired level the relay becomes unbalanced and The regulator automatically raises its output voltage to compensate for the drop and continues to do so until relay 16 is again balanced. Relay 16 and the regulator cooperate in a similar manner when the output voltage of the regulator is too high.

It is generally desirable to occasionally test the accuracy of relay 16 in responding to the predetermined voltage range. This invention provides a means for providing a test voltage or meter voltage V as referred to in FIG. 3, which simulates voltages normally obtained from potential transformer 14, thus eliminating the need for altering the output voltage of the regulator and potential transformer 14 which would adversely affect the operation of the regulator. In normal operation a movable contact 22 rests on contact 23. Inasmuch as the compensator is not needed in testing the relay it is switched out by moving contact 27 from contact 28 to contact 29, thus short circuiting current transformer 21. In order to test relay 16, contact 22 is moved over to contact 24, causing the insertion of a series connected capacitance 26. The moving of contacts 22 and 27 may be simplified by mechanically linking them, enabling one to move both contacts simultaneously. Such mechanical linkage is preferable also as a protective measure for if the current transformer is not short circuited an undesirable high voltage may occur across the current transformer primary winding.

A voltmeter 31 is connected in parallel with the impressed voltage and the series connected load and indicates the voltage of the potential circuit 11 which influences relay 16. Prior to the insertion of capacitance 26 voltmeter 31 reads the impressed voltage V; of transformer 14- or the vectorial addition of I R and I X vectorially shown in FIG. 3. As illustrated, the current I of the circuit when capacitance 26 is electrically isolated from the circuit lags voltage V; at an angle a. This is a result of the lagging effect of the inductance obtained from variable inductance 18 and the coil of relay 16. However, upon adding capacitance 26, the new current, now referred to as I in the potential circuit lags the voltage V at a smaller angle b. As mentioned previously and illustrated in FIG. 1, insertion of capacitance 26 reduces the total impedance of the circuit and, consequent- 1y, I is greater than 1 Therefore, the new resistive component 1 R and new inductance component I X are both greater than their original values. With capacitance 26 inserted in the circuit, voltmeter 31 no longer reads the impressed voltage of transformer 14, but now reads the vectorial addition of 1 R and I X The test or meter voltage V which is now affecting relay 16 and is read on the voltmeter is of a larger value than V the original impressed voltage aifecting relay 16. V may also be read as the vectorial addition of V; and I X Means must also be provided for obtaining a voltage reading less than V; in order to test the effectiveness of relay 16 in reacting to a subnormal voltage. This is accomplished by connecting variable resistance 32, preferably a rheostat, in series with capacitance 26 and relay 16. Movable contact 22 is adjusted on resistance 32 until the voltmeter reads the desired value. The insertion of more resistance into the circuit causes the resistive component 1 R of FIG. 3 to become smaller since I is now smaller. Consequently, V is also reduced in magnitude.

Upon completion of the relay test movable contacts 22 and 27 are returned to stationary contacts 23 and 28, respectively, and, consequently, voltage sensitive relay 16 is restored to its normal operating condition. Unlike tests of the prior art there is no need for resetting and adjusting variable inductance 18 and variable resistance 19. Nor has the output voltage of the regulator been altered at any time during the test or calibration of the relay.

While but only one embodiment of this invention has been described it will be obvious to those skilled in the art that modifications can be made within the scope of the appended claims and that a relay is merely illustrative-0 f other reactive voltage sensing devices such as contact making motors and magnetic amplifiers used in various types of regulating systems.

What is claimed is:

1. In an electrical regulating apparatus: a linear reactance circuit having a voltage sensitive device, a reactance of opposite phase displacement from said linear reactance circuit, a variable resistor connected to said opposite phase reactance, and a switching means for selectively switching said variable resistor and reactance in and out of said reactance circuit for raising the voltage across said circuit to a first value and lowering the voltage across said circuit to a second value to test the response of said voltage sensitive device to voltages between said first and second values.

2. In an electrical regulating apparatus: a linear reactance circuit having a voltage sensitive device responsive to a signal of a varying voltage, a reactance of opposite phase displacement from the linear reactance of said circuit, means for inserting said opposite phase reactance into said linear reactance circuit whereby the voltage across said circuit is raised to a value substantially equal to the highest expected signal voltage, and a variable resistor connected with said reactance to vary the voltage across said linear reactance circuit to a value substantially equal to the lowest expected signal voltage to test the response of said voltage sensitive device.

3. In an electrical regulating apparatus a reactance circuit having a voltage sensitive device responsive to a signal of a varying voltage, a reactance of opposite phase displacement from the reactance of said circuit having one end connected to said circuit, the other end of said opposite phase reactance connected to a variable resistor, and a single means for selectively inserting said reactance and variable portions of said resistor to said linear reactance circuit whereby the voltage across said circuit may vary from a value substantially equal to the highest expected signal voltage to a value substantially equal to the lowest expected signal voltage.

4. In a voltage regulating apparatus: a linear inductive circuit having a voltage sensitive device connected across a source of a signal of a varying voltage, a capacitor connected at one end to said linear inductive circuit, the other end of said capacitor connected to a variable resistor, a movable contact connected to said circuit for switching said capacitor in series with said circuit to raise the voltage across said voltage responsive device to a value substantially equal to the highest expected signal voltage, said movable contact further operable across the full range of said variable resistor to vary the voltage across said device to a value substantially equal to the lowest expected signal voltage to test the response of said device.

References Cited in the file of this patent UNITED STATES PATENTS 2,668,942 Varela Feb. 9, 1954 2,906,942 Mittag Sept. 29, 1959 FOREIGN PATENTS 110,785 Australia Oct. 10, 1928 431,422 Great Britain July 8, 1935

Images