Protective switch with status detection

A protective switch assembly (100) includes switch position sensors (109) that sense switch blade (14) position and indicate whether one or more switches (104) are open. According to another aspect, the voltage and current of the switch circuits are monitored to determine switch position as well as overall circuit status.

FIELD OF INVENTION

The present application is directed to protective relay switches, and more particularly to test switches having status detection means.

BACKGROUND

Protective relays are commonly used in electric utility applications to detect various possible problems in the electrical power output and thus protect expensive equipment such as motors and generators. Protective relays continuously monitor power systems to assure maximum continuity of electrical service with minimum damage to life and property.

Some of today's protection applications are, without limitation: motor, generator, transformer, station-bus, line and circuit, system ground, network systems, pilot wire, pilot channel, transmission line, pilot relying, backup, reclosing, synchronizing, load-shedding, frequency and many more. Typically, protective relays, meters and instruments receive their input signals from sensors (commonly current transformers and potential transformers) which step down the high current and voltages and provide a proportional output signal.

The relay terminals are connected to the transformers/sensors through a test switch terminal or “poles”. Each test switch can be associated with one or more relays. Test switches provide the necessary short circuiting of line and load terminals when the relay is removed from its case or the adjacent test switch is opened. In this manner, the test switch disconnects the protective relay from the sensors for the purposes of calibration and/or replacement. Thus, test switches are the means by which protective relays are disabled. Additionally, test switches provide an access point for maintenance personnel to directly measure current/potential values using meters, for example, test plugs.

An exemplary prior art test switch assembly is shown inFIG. 1and generally indicated by the numeral10. The wide variety of test switches available allows for many types of applications. As is well known to those of ordinary skill in the art, these applications may include test switches with all potential switches, all current switches or some combination thereof.

Test switch assembly10includes on its front face10switches12ato12jarranged in five (5) sets. In the embodiment shown inFIG. 1for prior art test switch10there are two switches, namely switch12aand12b, which are associated with a respective current transformer (not shown). Test switch10also includes eight (8) potential switches, namely switches12cand12d,12eand12f,12gand12h,12iand12j.

One example of a pair of switches associated with a current transformer is shown inFIGS. 2aand2b. The paired switches include a switch, such as switch12awhich has a shorting blade14having a handle26(switch12a, when unpaired, may be a potential switch) and a switch12bwhich does not have a shorting blade and instead includes a test jack16. The input from the current transformer is connected to the bottom connector17of switch12a. The electrical current travels through shorting blade14and out the top connector18of switch12a, which is in turn electrically connected to a relay. The electrical current travels back from the relay, to top electrical connector19, through test jack16and back to the current transformer through the bottom electrical connector20of switch12b. A shorting tab22extends from the bottom of switch12bto a location beneath switch12a. Shorting tab22is electrically connected to bottom connector20of switch12b.

During normal operation, with the shorting blade14closed, electrical current flows from the current transformer to, bottom connector17, through the shorting blade14, to the top connector18and from there to the relay. The electrical current returns from the relay through to connector19, through the test jack16, to the bottom connector20, and from there, to the transformer. If, however, an operator wishes to remove the current signal from the relay, the shorting blade14is opened. As the blade14is rotated, and before it is electrically disconnected from top connector18, a bottom edge24of shorting blade14engages the shorting tab22, thereby electrically connecting bottom connector17with bottom connector20. Thereafter, the blade14disconnects from top connector18and the current signal to the relay is stopped. By shorting out the circuit first, the current always has a path to travel, thereby preventing dangerous voltage buildup in the transformer.

On the rear face of test switch assembly10, twenty terminals are provided for connection to the relays and sensors/transformers. When test switch10is mounted in a switchboard panel (not shown) the switches12ato12jare accessible from the front of the panel and the terminals on the rear face are only accessible from the rear of the panel.

Though prior art test switches have proved remarkably dependable, drawbacks persist. For example, in some instances a maintenance person could disable a relay (via the test switch), for troubleshooting or maintenance purposes. The power system may be restored and the test switch unintentionally left in a configuration that disables the device. Such conditions could cause the protection and control equipment to fail.

Other potential issues exist that may affect relay performance, such as blown fuses, changed wires, or changes to the topology of the protection and control scheme (either intentional or unintentional). Any of these conditions may lead to incorrect operations or failures of the relay. It is therefore desirable to verify all the correct signal inputs to the test switch prior to restoration of the power system.

SUMMARY OF THE INVENTION

According to one aspect of the present invention a switch assembly is provided for selectively opening and closing the electrical connection between a protective relay and a potential or current sensor. The switch assembly includes a plurality of individual switches including blades movable between an open and a closed position, the switches being electrically connected between the protective relay and the potential or current sensor. A switch position sensor is positioned proximate to the blade in each of the plurality of individual switches to sense when the blade is in the open or closed position. An indicator optically displays whether any one of the blades is in the open position based on signals from said switch position sensors.

According to another aspect of the present invention, a system is provided for selectively opening and closing the electrical connections between one or more protective relays and a potential or current transformer. The system includes a plurality of switch assemblies each including a plurality of individual switches including blades movable between an open and a closed position. The switches are electrically connected between the protective relay and the potential or current transformer. Each switch assembly includes at least one sensor to monitor the signal from the potential or current transformer. A monitoring module is in communication with the at least one sensor. The monitoring module determines from the output of the sensor, whether at least one of said switches is open or closed.

DETAILED DESCRIPTION OF THE INVENTION

With reference now toFIG. 3, an exemplary installation100is shown, including a plurality of switch assemblies102. Switch assemblies102each include a plurality of individual switches104that are modular and horizontally stackable to provide flexibility and efficiency. Each switch assembly102includes a plurality of individual switches104(seeFIG. 4) arranged in a logical grouping and covered by a movable safety cover. For example, one switch assembly102amay include switches104for differential protection for a transformer. A second switch assembly102bmay include switches104for the primary protection for a transformer. A third grouping102cmay include switches104for backup protection for a transformer. Another logical grouping102dmay include switches104for all protection for a given transformer. Any number of groupings may be used, to provide a convenient interface for an operator.

With reference now toFIG. 4, as discussed above, each switch assembly102includes a plurality of switches104that may be modular and stackable. Inner switches104aare bounded on each side with end switches104b. With reference now toFIG. 5, in order to improve clarity, a switch assembly102is shown with the electrical components of all but one switch removed. As can be seen, the switch includes a sensor108positioned proximate to the handle26of the blade when in the closed position. Sensor108detects the presence of the pivotable blade14when in the closed position. Sensor108may be one of a plurality of types of proximity sensors. For example, sensor108may be an RF sensor, wherein an RFID tag is secured to the handle or blade. According to this embodiment, when blade14is pivoted to the open position, the RFID tag will go out of the range of the receiver triggering a status change. According to another embodiment, the sensor108may be a hall sensor which detects a small magnet positioned on the blade14or handle26. According to yet another embodiment, sensor108may be an optical sensor that detects when the blade or handle is in the closed orientation.

Each switch assembly102includes a switch position indicator112(seeFIG. 4) that indicates if any of the switches in the switch assembly are in the open configuration. According to one embodiment, indicator112may include one or more LEDs capable of alternately emitting a green or red light. According to one embodiment, if all sensors108of a switch assembly102sense their respective switch in the closed configuration (e.g. blade14at approximately90degrees closing the electrical connection between a bottom and top electrical connector) the indicator112emits a green light. However, if any one of the sensors108detects that their respective switch104is in a position other than closed (i.e. blade14pivoted away from the switch assembly as shown inFIG. 4), the indicator112emits a red light. Each switch assembly102includes a cover114that pivots between an open (seeFIG. 4) and closed (seeFIG. 3) position. Cover114may be clear or opaque. Accordingly, to accommodate an opaque cover, the indicator112is positioned outside of the area covered by cover114so that an operator can see the indicator112even when cover114is closed.

The sensor108and indicator112may draw power from the circuit to being monitored or, preferably, receives power from a power module116. As shown inFIG. 6, a single power module116may provide power for all switch assemblies102in an installation100. According to other embodiments, a power module116may be provided for each switch assembly102.

Each installation100may also include a monitoring module120that is in electrical communication with sensors108. Monitoring module120may accordingly provide a separate indicator122that indicates if any one of the switches104in the installation100is open. In order to minimize data transfer size and simplify interpretation, each switch assembly102may provide a single signal indicative of the overall status of the switches to the monitoring module120. The output from each switch assembly102may be a binary signal (good/bad or high/low). Monitoring module120is capable of receiving status signals from multiple switch assemblies and in turn is in communication with a control room or other remote location to transmit switch status information.

Monitoring module120may further facilitate the direct monitoring of the signals being output from the instrument transformers (as will be discussed below in greater detail). Directly monitoring the circuit between the relay and the instrument transformers provides many advantages. Specifically, this approach enables the detection of additional causes of faulty operation, for example a blown fuse on a potential transformer. Signal measurement at the switch can determine not only that the test switch is in the correct closed position but also that the proper signals are applied to the relay prior to power system restoration. The use of the signal measurements on the switch opens the new possibilities to diagnose problems on current and potential transformers. Until now there has been little focus on what may be the weakest link of the power system. If the instrument transformers cannot accurately replicate the conditions of the primary power system due to failures or degradation, such systems and associated protection and control schemes will be compromised.

The reading of the voltages and currents from a current transformer can provide valuable information to calculate baseline values that can be compared to future operating values and monitor degradation of the products. Similarly, on potential circuits, industry practice is to only read voltages. Thus, according to one aspect of the invention, each switch includes integrated voltage and/or current sensors in accordance with the configurations shown below. The sensor measurements may be transmitted to the monitoring module120where analysis may be performed and/or the data is transmitted to remote locations.

With reference now toFIG. 7, in a potential switch, the current is monitored at A to determine the status of the switch (opened or closed). According to this embodiment, the presence of current at A indicates a closed pole and the absence of current at A indicates an open pole.

With reference now toFIG. 8, in a potential switch, the differential voltage is monitored across the switch to determine the status of the switch (opened or closed). According to this embodiment, a zero or very low voltage reading (nominal absence of voltage) indicates a closed switch. A nominal voltage reading (or nominal presence of voltage) indicates an open switch.

With reference now toFIG. 9, in a potential switch, the voltage is measured across the switch relative to a common ground or other reference point in the system. This approach has the added advantages of eliminating the possibility of floating voltages, and the system voltages can be read directly and used for other purposes. According to this embodiment, if V1is subtracted from V2, resulting in a zero or very low voltage reading, this indicates a closed switch. If V1has a zero voltage reading, but V2has a non-zero voltage reading, this indicates an open switch. If both V1and V2have a zero or very low voltage reading, this indicates that system power is off. Thus, in the embodiment ofFIG. 9, it is possible to differentiate between an open, closed and power system off condition.

With reference now toFIG. 10, in a potential switch, the voltage is measured across the switch and the current is measured at A. This method uses both current and voltage measurements to monitor switch status. According to this embodiment, the absence of current at A along with a voltage across the switch indicates an open switch. The presence of current at A along with the absence of a voltage across the switch indicates an open pole. When no signal is received from the power system, both the voltage and current will read zero. In this manner, each of the three system statuses (switch open, switch closed, no signal from the transformer) are distinguishable. Accordingly, this arrangement does not have the limitation of incorrect indications when the power system is off.

With reference now toFIG. 11, in a potential switch, the current is measured at A and the voltage is measured across the switch relative to a common ground or other reference point in the system. According to this embodiment, the absence of current at A along with a differential voltage (V2−V1) that is other than zero indicates an open switch. The presence of current at A along with a voltage differential (V2−V1) that has a zero or very low voltage reading indicates a closed pole. When no signal is received from the power system, both the voltage and current will read zero. In this manner, each of the three system statuses (switch open, switch closed, no signal from the transformer) are distinguishable. Further, this configuration eliminates the possibility of floating voltages. Also, the voltage values may be read directly and used for other monitoring functions.

With reference now toFIG. 12, in a ganged current switch, the current is measured at two locations. The current is measured at A1on the relay side (load side) and at A2on the current transformer side (source side). According to this embodiment, the presence of similar current readings (A1=A2) indicates the switch is closed (normal operation). If a positive current is measured at A2but A1reads zero or very close to zero, this indicates that the switch is open. If both A1and A2measure zero, this indicates no current signal is being output from the transformer (sensor).

With reference now toFIG. 13, in a ganged current switch, the voltage is measured across the shorting blade switch. If the voltage measurement is zero or very low, this indicates the switch is closed in the normal operating position. If a voltage is measured across the switch, this indicates that the switch is open.

With reference now toFIG. 14, in a ganged current switch, the voltage is measured relative to ground or a reference point on the load side and supply side of the switch. It has the added advantages of eliminating the possibility of floating voltages, and the system voltages can be read directly and used for other purposes. According to this embodiment, if V1=V2, this indicates the switch is closed in normal operation. If V1does not equal V2, this indicates the switch is open.

With reference now toFIG. 15, in a ganged current switch, current at both the load and supply side of the switch are measured, as well as voltage across the switch. During a closed switch (or normal) operation, the presence of similar current readings at A1and A2validates a normal operation (closed switch). This is re-validated by the voltage measurement, where absence or very low voltage indicates a closed switch. During an open switch (shorted CT), dissimilar current readings (presence of current at A2and no current at A1) indicates an open switch(shorted CT). This is re-validated by the voltage measurement, where a presence of voltage indicates an open switch. If no current is measured at either A1or A2, but a voltage is developed across the switch, this indicates an open current transformer, (i.e. the switch is open but not short-circuited) a potentially dangerous condition.

With reference now toFIG. 16, in a ganged current switch, current at both the load and supply side of the switch are measured. Also, the voltage is measured relative to ground or a reference point on the load side and supply side of the switch. During a closed switch (or normal) operation, the presence of similar current readings at A1and A2validates a normal operation (closed switch). This is re-validated by the voltage measurement, where if V1=V2this indicates a closed switch. During an open switch (shorted CT), dissimilar current readings (presence of current at A2and no current at A1) indicates an open switch (shorted CT). This is re-validated by the voltage measurement, where a presence of voltage at V1but not at V2indicates an open switch. If no current is measured at either A1or A2, but a voltage is developed at V1, this indicates an open current transformer, (i.e. the switch is open but not short-circuited) a potentially dangerous condition.

With reference now toFIG. 17, in a ganged current switch, only two measurements are made, one voltage and one current. The minimal number of sensors make this embodiment economically advantageous. Current is measured at the supply side of the switch and voltage is measured across the current transformer. A switch sensor configuration according to this embodiment is capable of detecting closed blade (normal operation), open blade (shorted CT), power off, and can also detect an open current transformer condition at any location in the circuit.

According to this embodiment, a positive current and non-zero voltage will be measured when the switch is closed in normal operation. If the switch is open in a shorted CT configuration, a positive current will be measured but the measured voltage will be zero or very close to zero. In an open current transformer condition, zero current will be measured, however a voltage will be seen. In a zero power situation, zero voltage and current will be measured.

According to this embodiment, in addition to the monitoring functions, a set of failsafe contacts may be provided to short the test switch terminals (across V) if an open CT condition is identified. This provides added safety to the user and avoids damage to downstream devices (like the protective relay). This failsafe contacts may also be provided at the current transformer terminal instead of the switch.

Other configurations are contemplated, wherein the voltage and current are measured at a single location each. For example, with reference now toFIG. 18, a monitoring configuration is shown which is substantially the same asFIG. 17, however, instead of measuring voltage across the current transformer, the voltage is monitored at the input or output of the CT relative to ground or a reference voltage.

According to this embodiment, a positive current and non-zero voltage will be measured when the switch is closed in normal operation. If the switch is open in a shorted CT configuration, a positive current and voltage will also be measured. In an open current transformer condition, zero current will be measured, however a voltage will be measured. In a zero power situation, zero voltage and current will be measured.

As will be appreciated by one of ordinary skill in the art, various functions in the present invention may be embodied as or take the form of a computer readable medium having computer-readable instructions stored thereon which, when executed by a processor, carry out the operations of the present inventions as previously described. The computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the user-interface program instruction for use by or in connection with the instruction execution system, apparatus, or device and may by way of example but without limitation, be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium or other suitable medium upon which the program is printed. More specific examples (a non-exhaustive list) of the computer-readable medium would include: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device. Computer program code or instructions for carrying out operations of the present invention may be written in any suitable programming language provided it allows achieving the previously described technical results.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention. It is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.