Patent Application
20140265637
The present disclosure relates generally to bypassing a voltage regulator in a power system. More specifically, the present disclosure relates to preventing a voltage regulator from being bypassed when certain safe bypass conditions are not met.
The practice of bypassing a regulator is fairly common. Bypassing is done in order to avoid power disruptions when installing or removing a regulator from service. If it is not done properly, i.e.—the regulator is bypassed while the tap changer is not in the neutral position (commonly referred to as “Bypass off Neutral”), serious damage can result. When the tap changer is not in the neutral position, a voltage exists between the source and load bushings of the regulator. Bypassing the regulator creates a short circuit between the source and load bushings through the bypass switch. If the series winding has not been taken out of the circuit by moving the tap changer to the neutral position, the voltage across the source and load bushings can drive a very large current through the regulator series winding and bypass switch. This large current can burn insulation, create arcing, melt windings, and lead to a rupture of the regulator tank. Because of the typically small number of series turns involved, the ratio of series turns to shunt turns can be very small. This means that even though a very large bypass current is flowing in the series winding, a much smaller current is reflected into the shunt winding. This current can be near or below rated load current. As a result, upstream protection may, be unable to detect the situation until a ground fault occurs. Therefore, the protective equipment upstream of the device often cannot sense and/or cannot respond quickly enough to prevent the failure from becoming catastrophic.
Traditionally, the method for ensuring a safe bypass operation is a manual process in which the user is recommended to verify that the regulator tap changer is in the neutral position and no voltage differential is present between the load and source sides of the bypass switch and voltage regulator. Typically, such verification includes four possible methods: 1) verify that a neutral indicator light on the control is indicating the neutral position; 2) verify that the tap position display on the regulator control interface indicates the neutral position; 3) verify that the mechanical position indicator on the regulator is in the neutral position; and 4) verify by measurement that there is no voltage difference between the source and load bushing. Such methods are typically dependent upon the observation, judgment, knowledge, and conscientiousness of the user. Thus, such existing methods can be prone to human error.
In an example embodiment, a system with voltage regulator bypass includes a voltage regulator, a bypass switch coupled to the voltage regulator, and between a source and a load, the bypass switch comprising a first state and a second state. In the first state, the bypass switch electrically couples the source to the voltage regulator and the voltage regulator to the load, establishing a conductive path between the source and load via the voltage regulator.
In the second state, the bypass switch electrically couples the source directly to the load, bypassing the voltage regulator. The system further includes a bypass switch controller coupled to the bypass switch, wherein the bypass switch controller controls whether the bypass switch is put into the first state or the second state, and a voltage regulator controller coupled to the bypass switch controller and the voltage, regulator, wherein the voltage regulator controller prevents the bypass switch controller from putting the bypass switch into the second state unless one or, more bypass conditions are met.
In another example embodiment, a voltage regulator bypass controller includes a logic controller configured to couple to a bypass switch controller, wherein the bypass switch controller is coupled, to and controls a bypass switch. When the logic controller is coupled to the bypass controller, the logic controller prevents the bypass switch controller from actuating the bypass switch unless one or more bypass conditions are met.
In another example embodiment, a method of bypassing a voltage regulator includes receiving a plurality of inputs from a voltage regulator, and determining if a bypass condition has been met based on at least the inputs from the voltage regulator. If it is determined that the bypass condition is met, then permit a bypass switch controller to actuate a bypass switch and put the voltage regulator into a bypassed state. If it is determined that the bypass condition is not met, then prevent the bypass switch controller from actuating a bypass switch. The method further includes, preventing the voltage regulator from being put into the bypassed state.
For a more complete understanding of the example embodiments of the present disclosure and the advantages thereof, reference is now made to the following description in conjunction with the accompanying drawings in, which:
The drawings illustrate only example embodiments of the disclosure and are therefore not to be considered limiting of its scope, as the disclosure may admit to other equally effective embodiments. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of example embodiments of the present disclosure. Additionally, certain dimensions may be exaggerated to help visually convey such principles.
Embodiments of the disclosure are directed to systems and methods for bypassing a voltage regulator in a power system when the voltage regulator is in a neutral state and no voltage differential exists between source and load bushings of the voltage regulator. In the description, well known components, methods, and/or processing techniques are omitted or briefly described so as not to obscure the disclosure. As used herein, the “disclosure” refers to any one of the embodiments described herein and any equivalents, but is not limiting to the embodiments described herein. Furthermore, reference to various feature(s) of the “disclosure” is not to suggest that all embodiments must include the referenced feature(s). The following description of example embodiments refers to the attached drawings.
Turning now, to the drawings, in which like numerals indicate like elements throughout, example embodiments of the disclosure are described in detail.
Turning to
In the example embodiment shown in
In an example embodiment, the bypass switch control 110 is locked from putting the bypass switch 104 into the on mode if the voltage regulator is not in a neutral state, as determined by the voltage regulator controller 112. Specifically, an output signal from the voltage regulator controller 112 is sent to the bypass switch control 110. The output signal is an indication of whether the voltage regulator is in a neutral state. When the voltage regulator is in the neutral state, there is effectively no voltage difference between the voltage provided to the voltage regulator 108 from the power source 102 and the voltage provided to the load 106 from the voltage regulator 108. Thus, if the voltage regulator 108 were to be bypassed, there would be effectively no voltage difference between the power source 102 and the load 106, and thus, generally no harmful current surge.
An output signal 116b is generated by the voltage regulator controller 112 in response to one or more voltage measurements at the voltage regulator 108. Specifically, if, it is detected that the voltage regulator 108 is in the neutral state, the voltage regulator controller 112 sends a signal to the bypass switch control 110 which unlocks the bypass switch control 110, allowing it to put the bypass switch 104 into the on mode, thereby bypassing the voltage regulator 108. However, if it is detected that the voltage regulator 108 is not in the neutral state, the voltage regulator controller 112 sends a signal to the bypass switch control which locks the bypass switch control. When the bypass switch control 110 is locked, it is generally unable to put the bypass switch 104 into the on mode, and the voltage regulator 108 cannot be bypassed. Thus, in general, the voltage regulator 108 can only be bypassed when the voltage regulator 108 is in the neutral state. Various voltage measurement circuits and methods are employable for detecting the neutral state of the voltage regulator 108 in addition to those disclosed herein. In certain example embodiments, in order for the voltage regulator controller 112 to make a neutral determination of the voltage regulator 108, one or more additional conditions must be met, a subset of which is detailed below.
In an example embodiment, the voltage regulator 108 includes a differential potential transformer 202, a potential transformer 204, an auto-transformer 206, and a tap changer 208. In an example embodiment, the auto-transformer 206 is the combination of a shunt winding 212 and a series winding 214. The series winding 214 includes a plurality of taps, and the shunt winding 212 has a fixed ratio to a control winding 210. The tap changer 208 includes movable contacts 220 and stationary contacts 216 individually connected to taps, of the series winding 214. In an example embodiment, the series winding 214 is physically located outside of the tap changer 208. The movable contacts 220 are configured to make contact with one or two of the stationary contacts 216 at a time, thereby effectuating a variable number of windings in the series winding 214. The stationary contacts 216 includes a neutral contact 218, which effectively bypasses the series winding 214. Thus, when the movable contacts 220 are coupled to the neutral contact, no portion of the series winding 214 is, connected between the source and load bushings 232, 230, and the voltage regulator is in the neutral state. Specifically, the series winding 214 and the neutral contact 218 are coupled to the load bushing 230, and the movable contacts 220 is coupled to the source bushing 232. The load bushing 230 is coupled to the load via the bypass switch 104 and the source bushing 232 is coupled to the power source 102 via the bypass switch 104. When the movable contacts 220 are coupled to the neutral contact 218, the load 106 is coupled to the power source 102 via the bypass switch, without going through any windings 214. Thus, the voltage provided at the power source 102 is effectively the same as the voltage provided at the load 106, and the voltage regulator 108 is in the neutral position.
The movable contacts 220 can be further coupled to a preventative autotransformer 222 or other form of impedance to prevent a short circuit condition when the movable contacts 220 are bridging across taps 216 at different electrical potentials. In an example embodiment, the preventative autotransformer 222 is located outside of the tap changer 208. In certain example embodiments, the tap changer 208 also includes a polarity switch 226. The polarity switch 226 is used to couple the load bushing 230 to either a first end 215a of the series windings 214 or a second end 215b of the series winding 214, which determines whether the series windings 214 has an additive or subtractive effect on the voltage.
In certain example embodiments, further detection of the voltage regulator 108 being in the neutral state employs the differential potential transformer 202 and/or the potential transformer 204. In certain example embodiments, the signals of differential potential transformers 202 coupled in the circuit are used to detect the neutral state. In certain example embodiments, the differential potential transformer 202 is used to measure the voltage difference across the source-side, or source bushing 232, of the voltage regulator and the load-side, or load bushing 230, of the voltage regulator. The measured voltage difference by the logic controller 256 and a neutral state determination is made by the logic controller 256. Specifically, if the measured voltage difference is below a set threshold, it is an indication the voltage regulator 108 is in the neutral state. Conversely, if the measured voltage difference is not below the threshold, then it is an indication that the voltage regulator 108 is not in the neutral state. The voltages at the source bushing 232 and the load bushing 230 of the voltage regulator can also be measured separately against a reference point, for instance, by using the control winding 210 and the potential transformer 204, and comparing the values.
It should be noted that
In certain example embodiments, the voltage regulator 108 is, a type A voltage regulator, in which the shunt winding 212 is coupled to the source 102. In such an embodiment, the system 100 includes the differential potential transformer 202, through which a neutral state can be detected. In certain example embodiments, the voltage regulator 108 is a type B voltage regulator, in which the shunt winding 212 is coupled to the load 106, and the control winding 210 to monitor the voltage on the load 106. In such an embodiment, the potential transformer 204 may not be included in the system 100.
In certain example embodiments, the tap changer 208 also includes a neutral position switch 224. The neutral position switch 224, is typically triggered when the neutral tap 218 is selected and coupled to the movable contacts 220. The neutral position switch 224, when triggered, provides a signal to the logic controller 256 indicative of the neutral tap 218 being selected. In certain example embodiments, the power system 100 includes a neutral position indicator light 234. The indicator light 234 may be powered directly from the neutral position switch 224 or from the logic controller 256, and lights up when the tap changer 208, and thus voltage regulator 108, is in the neutral state.
Under normal operating conditions (i.e., when the bypass switch 104 is in the off mode), the bypass switch 104 connects the power source 102 to the source bushing 232 through a source disconnect contact 236. The load 106 is connected to the load bushing 230 through a load disconnect contact 238. The bypass switch 104 further includes a bypass contact 240. The bypass contact 240 is coupled between the load 106 and the power source 102 such that when the bypass contact 240 is open, the load 106 is not electrically coupled to the power source 102 via the bypass contact 240. When the bypass contact 240 is closed, the load 106 is directly electrically coupled to the power source 102 via the bypass contact 240. Thus, in order to prevent a short circuit across the series winding 214, the bypass contact 240 remains open while the regulator is in service (i.e., not bypassed). In an example embodiment, the source disconnect contact 236, the load disconnect contact 238 and the bypass contact 240 may or may not be ganged together to operate through a single actuator 242. Specifically, the actuator 242, when operated on, either opens the disconnect contacts 236, 238 and closes the bypass contacts 240, or closes the disconnect contacts 236, 238 and opens the bypass contacts 240. In certain example embodiments, the actuator 242 is a mechanized actuator. In certain other example embodiments, the actuator 242 is an electrical switch.
In an example embodiment in which the actuator 242 is a mechanized actuator, the actuator 242 is controlled by the bypass switch controller 110. The bypass switch controller 110 includes a control switch 248, a power supply 246, and a safety relay 250. Specifically, in an example embodiment, the control switch 248, the safety relay 250, and the power supply 246 are coupled serially with the actuator 242. Thus, the actuator 242 is powered by the power supply 246, and actuated, when the control switch 248 and the safety relay 250 are both in the closed position. If either of the control switch 248 and the safety relay 250 are open, then an open circuit occurs and the actuator 242 is not powered. In certain, example embodiments, the default state of the actuator 242 is a normal state, in which the load disconnect contact 238 and the source disconnect contact 236 are closed and the bypass contact 240 is open (i.e., voltage regulator not bypassed). When actuator 242 goes into a bypass state when it is powered, the load disconnect contact 238 and source disconnect contact 236 are opened and the bypass contact 240 is closed. Thus, in an example embodiment, both the control switch 248 and the safety relay have to be closed, or activated, for the actuator to be put into the bypass state.
The control switch 248 is activated when it is determined, either automatically or by, a user, that the voltage regulator 108 is to be bypassed and the load 106 is to be directly coupled to the power source 102. Thus, in certain example embodiments, the control switch 248 is coupled to and/or follows a button or the like or a user interface. In certain example embodiments, the control switch 248 is coupled to and/or responds to a signal from a processor or controller. In an example embodiment, the safety relay 250 is controlled by the logic controller 256. Specifically, the logic controller 256 generates a safe output signal when the controller detects that one or more safe bypass conditions are met. The safe output signal is sent to the safety relay 250 and activates the safety relay 250 to be a closed circuit component. Thus, when the control switch 248 is activated (i.e., closed), the circuit is completed and the actuator 242 is actuated. In an example embodiment, the safety relay 250 is disabled (i.e., open) by default when the controller 112 does not detect that bypass conditions are met and thus does not send the safe output signal to the safety relay 250. Thus, the safety relay 250 remains open when bypass conditions are not met, and the actuator 242 cannot be activated even if the control switch 248 is enabled. The safety relay 250 described herein is an example actuator 242 hocking mechanism. Various other implementations of an actuator 242 locking mechanism which disables the actuator 242 from being activated even when then control switch 248 is activated are applicable and considered to be within the scope of the disclosure.
As discussed above, in certain example embodiments, the logic controller 256 enables the safety relay 250 when one or more bypass conditions are met. The bypass conditions are determined from one or more of various inputs 252 to the logic controller 256. Most crucially, the logic controller 256 should verify, that the voltage across the load and source sides of a regulator bypass switch 104 is sufficiently small to eliminate the chance of a short circuit through the bypass switch 104 and voltage regulator 108. One method of verification of such is to utilize a differential potential transformer 202 or a similar measurement device to directly measure the difference in potential between the load bushing 230 and the source bushing 232. Another method of verification is to measure the voltages at the source and load sides of the voltage regulator 108 separately against a reference point, for example, using the control winding 210 and the potential, transformer 204, and comparing the values. Additionally, resistive dividers, capacitive dividers, and other commonly used voltage measurement means may be similarly used. Additionally, in certain example embodiments, when the voltage regulator 108 is currently being bypassed, the bypass switch 104 also cannot be switched out of the bypass position without proper output from the voltage regulator 108.
In certain example embodiments, in addition to detecting that the source and load voltages 232, 230 are substantially similar, certain other bypass conditions may be required to be met prior to determining that a safe bypass condition exists. For example, one such bypass condition is that the neutral position switch 224 is triggered, indicating that the movable contacts 220 of the tap changer 208 are positioned on the neutral tap 218. Further, another such bypass condition may be verification that a voltage regulator controller 112 is in an off-line mode so that voltage regulator 108 may, not switch tap positions 214 until placed online. In certain example embodiments, the power supply 246 and/or the control switch 248 are also communicatively coupled to the logic controller 256 to prevent bypassing if all safety requirements are not met. Further, in certain example embodiments, a timer or remote control could be incorporated into the logic controller 256 to allow personnel to be in a remote/secure, location when the bypass switch 104 is operated. Additionally, in certain example embodiments, the bypass switch 104 includes a bypass position switch 258. The bypass position switch 258 is linked to the bypass contacts 240 and provides feedback to the logic controller 256 and/or the voltage regulator controller 112 regarding the position of the bypass contacts 240. Thus, the voltage regulator controller 112 is inhibited from switching tap positions 214 unless the bypass contacts 240 are open. In certain example embodiments, the logic controller 256 and the voltage regulator controller 112 are separate controllers that are communicatively coupled. In certain other example embodiments, the logic controller 256 and the voltage regulator controller 112 are one and the same. In certain example embodiments, the bypass switch controller 110, the logic controller 112, and the voltage regulator controller 256, or any subset thereof, are implemented together as one subsystem. For example, in an embodiment, the bypass switch controller 110 and the voltage regulator controller 256 are activated by the logic controller 112, and the bypass switch controller 110 operates the bypass switch 104.
A second AND gate 318b receives a state input from the first AND gate 318a as well as the tap changer module status 308 and the control switch off status 310. Specifically, for the second AND gate 318b to produce an ON output, the first AND gate 318a must be ON, the tap changer neutral switch (block 308) must be closed, producing an ON output, and the control switch (block 310) must be off, producing an ON output.
The output of the second AND gate 318b is sent to an OR gate 320 along with the output of a third AND gate 318c. In order for the third AND gate 318c to produce an ON state, a control power switch of the voltage regulator 108 must be in an internal position (block 312) and no output voltage (block 314) from the control winding 210 is detected. In certain example embodiments, the control power switch of the voltage regulator 108 is either in the internal position or an external position. The internal position is an indication that the potential transformer sensing inputs 202, 204, and 210 are being received internally under normal operation. The external position is an indication that the potential transformer sensing inputs 202, 204, and 210 are not receiving power internally. In order to provide any operation of the voltage regulator 108 when it is bypassed, the voltage regulator 108 must be coupled to an external supply for control and motor power. Thus, an ON state at the control power internal status 312 is indicative of the needed potential transformer signals being online. The third AND gate 318c is in the ON state when there is no output voltage detected at the control winding 210 and the voltage regulator 108 is receiving proper potential transformer signals. Typically, when both of these conditions are met, it is an indication that the power system 100 is not powered or the power source 102 is not providing any power, and there is no voltage in the power system 100.
In an example embodiment, an ON output at the OR gate 320 is generally an indication that the overall safe bypass conditions are met, and the safety relay 250 is enabled, allowing the voltage regulator 108 to be bypassed if needed. Thus, in order for the OR gate 320 to be in an ON state, at least one of the second AND gate 318b and the third AND, gate 318c must be in the ON state. If the power system 100 is detected to be unpowered and no voltage is provided, the safety relay 250 is enabled. On the other hand, if conditions 302, 304, 306, 308, and 310, which generally relate to ensuring that the tap changer 208 is in the neutral position 218 and the voltage difference between the load side 230 and the source side 232 is below a certain threshold, indicate the presence of power or voltage, then the safety relay 250 will not be enabled and the voltage regulator 108 cannot be bypassed. In certain example embodiments, a subset of such conditions may be employed and additional conditions may be employed.
In
In certain example embodiments, the power system 100 includes a built-in bypass switch controller 110 and/or the logic controller 256. In certain example embodiments, the bypass switch controller 110 and/or the logic controller 256 are made as stand-alone devices that retro-fitted onto existing power systems or used interchangeably with more than one Although embodiments of the present disclosure have been described herein in power system.
Although embodiments of the present disclosure have been described herein in detail, the descriptions are by way of example. The features of the disclosure described herein are representative and, in alternative embodiments, certain features and elements may be added or omitted. Additionally, modifications to aspects of the embodiments described herein may be made by those skilled in the art without departing from the spirit and scope of the present disclosure defined in the following claims, the scope of which are to be accorded the broadest interpretation so as to encompass modifications and equivalent structures.
