A new electromagnetic bushing voltage divider

Abstract

The present application belongs to the field of large high-voltage transformer bushing voltage monitoring, and particularly relates to a novel electromagnetic bushing voltage divider, which comprises sequentially connected voltage input unit, step-down transformer T1, amplitude and phase modulation unit, double-winding output isolation transformer T2 and voltage output unit; the secondary coil of the step-down transformer T1, the output end of the amplitude and phase modulation unit and the output end of the voltage output unit are respectively connected with different terminals on terminal block P1. The present application is installed at the voltage tap part of the bushing, and through the adjustment of the switch state of the bushing voltage divider adjustment switch group, the secondary output voltage of the voltage divider is linearly proportional to the primary voltage borne by the bushing, the voltage division precision of 1 ‰ can be realized, the phase precision can be within 0.05° deviation, and further, the signal can be provided for grid synchronization, and the primary voltage can be monitored.

Description

Technical Field

[0001] This invention belongs to the field of bushing voltage monitoring of large high-voltage transformers. Specifically, it is a new type of electromagnetic bushing voltage divider that can keep the output voltage and input voltage in phase when the connected load is less than 300VA, with an output voltage amplitude and phase error of 1‰. Background Technology

[0002] In power systems, real-time measurement of primary high voltage is necessary to ensure stable operation. A typical solution for voltage measurement is to use voltage transformers to divide the voltage and obtain a proportionally smaller voltage signal, which is then used in electronic measuring equipment and relay protection devices. However, voltage transformers represent a significant cost in terms of size, cost, installation, and space requirements within substations.

[0003] Voltage transformer voltage division schemes include directly using a step-down transformer to measure voltage, and using a capacitor divider followed by voltage reduction and phase adjustment. The latter is widely used in high-voltage measurement, and is known as a capacitive voltage divider voltage transformer. For transformer bushings with voltage taps above 110kV, the bushing itself is an excellent capacitive voltage divider; therefore, a miniaturized voltage divider integrated with the transformer can be implemented using the capacitive voltage divider method.

[0004] Electromagnetic voltage dividers can output 300VA and can be connected to voltage relays, synchronizers, voltage measuring devices, etc., on their load side, providing users with a very economical voltage measurement solution. They are widely used in South American countries. However, South American countries use oil-immersed voltage dividers with adjustable voltage taps on the transformer and inductor, equipped with partial compensation capacitors. The adjustment of the transformer and inductor voltage taps simply uses ordinary switching switches, which can cause transient overvoltages in the entire device during transformer and inductor operation. Summary of the Invention

[0005] The purpose of this invention is to provide a simple, space-saving, economical and reliable solution for monitoring primary voltage of power, and to enable all adjustments to be made online without causing overvoltage or damage to internal equipment.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0007] A novel electromagnetic bushing voltage divider includes: a voltage input unit, a step-down transformer T1, an amplitude modulation and phase modulation unit, a dual-winding output isolation transformer T2, and a voltage output unit connected in sequence; the secondary coil of the step-down transformer T1, the output terminal of the amplitude modulation and phase modulation unit, and the output terminal of the voltage output unit are respectively connected to different terminals on the terminal block P1.

[0008] The voltage input unit includes: bushing equivalent high voltage capacitor C1, bushing equivalent low voltage capacitor C2, grounding switch Sg, and overvoltage protection surge arrester R1. The system voltage input terminal is grounded in sequence through the bushing equivalent high voltage capacitor C1 and the bushing equivalent low voltage capacitor C2. The bushing equivalent low voltage capacitor C2, grounding switch Sg, and overvoltage protection surge arrester R1 are connected in parallel with the primary coil of step-down transformer T1.

[0009] The amplitude and phase modulation unit includes: parallel capacitor bank Ca, parallel capacitor bank Cb, parallel capacitor bank Cc, phase-shifting inductor L1, and voltage monitoring relay group. The secondary coil a terminal of step-down transformer T1 is connected to the primary coil a terminal of dual-winding output isolation transformer T2 in sequence through parallel capacitor bank Cb and phase-shifting inductor L1. The secondary coil b terminal of step-down transformer T1 is connected to the primary coil b terminal of dual-winding output isolation transformer T2. The parallel capacitor bank Ca is connected in parallel across the two ends of the secondary coil of step-down transformer T1. The two ends of the primary coil of dual-winding output isolation transformer T2 are connected in parallel with the voltage monitoring relay group and the parallel capacitor bank Cc, respectively.

[0010] The parallel capacitor bank Ca, parallel capacitor bank Cb and parallel capacitor bank Cc are each composed of multiple parallel branches, and each branch consists of a switching switch and a capacitor connected in sequence.

[0011] The voltage monitoring relay group consists of four voltage monitoring relays KV1-KV4. The two ends of the coil of each voltage monitoring relay are connected in parallel with the primary coil of the dual-winding output isolation transformer T2. The contacts of each voltage monitoring relay are used to send a switching signal.

[0012] The voltage output unit consists of two sets of switch groups, each set of switch groups consists of three branches, and each branch has one switch. In the first set of switch groups, one end of each branch is connected to a contact of the primary winding of the dual-winding output isolation transformer T2, and the other end of the three branches is connected to different terminals on the terminal block P1. In the second set of switch groups, one end of each branch is connected to a contact of the primary winding of the dual-winding output isolation transformer T2, and the other end of the three branches is connected to different terminals on the terminal block P1.

[0013] The terminal connected to the secondary coil of the step-down transformer T1 is used to output the voltage OUT1 after being stepped down by the step-down transformer T1; the terminal connected to the output terminal of the amplitude modulation and phase modulation unit is used to output the voltage OUT2 after being processed by the amplitude modulation and phase modulation unit; the terminal connected to the output terminal of the voltage output unit is used to output two independent voltages, namely AC110V and AC63.5V, after being stepped down by the dual-winding output isolation transformer T2.

[0014] Based on a novel electromagnetic bushing voltage divider method, the voltage output from the bushing voltage tap is linearly reduced to between AC 90V and 200V via a voltage input unit and a step-down transformer T1. The amplitudes of the secondary output voltages OUT1 and OUT2 are adjusted by switching on the parallel capacitor bank Ca. The phases of the secondary output voltages OUT1 and OUT2 are adjusted by switching on the parallel capacitor bank Cb. The amplitudes and phases of the adjusted voltages OUT1 and OUT2 are balanced by switching on the parallel capacitor bank Cc. By increasing the capacitance of the parallel capacitor bank Cc, the voltage is filtered. The dual-winding output isolation transformer T2 outputs the filtered voltage as two independent voltages: AC 110V and AC 63.5V.

[0015] The voltage in the voltage divider is monitored by a group of voltage monitoring relays. Specifically, voltage monitoring relay KV1 is used for transformer live measurement; it activates and outputs a switching signal when the voltage in the voltage divider exceeds 50% of the standard voltage. Voltage monitoring relay KV2 is used for undervoltage monitoring; it activates and outputs a switching signal when the voltage in the voltage divider falls below 90% of the standard voltage. Voltage monitoring relay KV3 is used for overvoltage monitoring; it activates and outputs a switching signal when the voltage in the voltage divider exceeds 110% of the standard voltage. Voltage monitoring relay KV4 is used for overvoltage monitoring; it activates and outputs a switching signal when the voltage in the voltage divider exceeds 120% of the standard voltage.

[0016] The present invention has the following beneficial effects and advantages:

[0017] The T1 transformer of this invention is a dry-type transformer, effectively reducing the problems of later maintenance. Phase adjustment uses a capacitor and inductor in series, eliminating the need for multi-tap adjustment on the inductor, avoiding overvoltage, and increasing the reliability of equipment operation. Capacitor adjustment uses powers of 2 increments, up to 10, allowing the capacitance to increase by 1 every 1 from 1 to 1024, achieving a precision adjustment of 1‰. The combined adjustment of the three capacitor banks can achieve an overall adjustment precision exceeding 1‰. The series connection of the inductor and capacitor in the circuit acts as a bandpass filter, ensuring stable operation within a specific frequency range while minimizing the impact of harmonics on the output. Attached Figure Description

[0018] Figure 1 Schematic diagram of an electromagnetic bushing voltage divider circuit.

[0019] Among them, 1 is the voltage input terminal of the high-voltage bushing, 2 is the equivalent high-voltage capacitor C1 of the bushing, 3 is the equivalent low-voltage capacitor C2 of the bushing, 4 is the grounding switch, 5 is the overvoltage protection surge arrester, 6 is the price reduction transformer T1, 7 is the parallel capacitor bank Ca, 8 is the parallel capacitor bank Cb, 9 is the phase shifting inductor L1, 10 is the voltage monitoring relay (KV1, KV2, KV3, KV4), 11 is the double-winding output isolation transformer, and 12 is the parallel capacitor bank Cc. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0021] The circuit schematic of this invention is as follows: Figure 1 As shown, by connecting this device to the voltage tap of the bushing, precise phase and amplitude adjustment of the voltage can be achieved by adjusting the range switch. The voltage divider can output 110V and 63.5V AC voltages, and the secondary voltage output will be linearly proportional to the primary voltage of the bushing. A load of up to 300VA can be connected to the output side, achieving high-precision linear output. Voltage regulation can be achieved through filtering by adjusting the range switch, ensuring that the output signal contains almost only the fundamental frequency signal. The key design features of this product include the following:

[0022] The voltage of the bushing voltage tap is linearly stepped down to between 90V and 200V AC by transformer T1, so that the subsequent circuits of the bushing voltage divider can operate within a safer range.

[0023] By using the switching function of capacitor plate Ca, the secondary output voltage range can be significantly adjusted, and the phase adjustment is relatively weak.

[0024] By connecting inductor L1 in series with capacitor plate Cb, and switching the corresponding switch of capacitor Cb, the phase of the secondary output voltage can be significantly adjusted, and the voltage amplitude can be adjusted relatively weakly.

[0025] By using the switching function of capacitor plate Cc, the voltage amplitude and phase can be adjusted in a relatively balanced manner. As the capacitance connected to Cc increases, the filtering effect becomes more significant, making the waveform in the circuit closer to a sine wave.

[0026] The voltage is first reduced to below 200V by the T1 transformer, which will not cause significant harm to the human body.

[0027] The Ca capacitor plate is used as the main means of voltage amplitude adjustment between 90 and 200V.

[0028] By utilizing the Cb capacitor plate and the series inductor L1 to adjust the reactive power characteristics of the series circuit, the circuit can adjust the output voltage phase online to move in the leading or lagging direction.

[0029] The phase and amplitude of the output voltage can be adjusted again by using the switch of the Cc capacitor plate. Furthermore, the input of Cc will enhance the low-frequency filtering effect in the circuit, which can significantly filter out high-order harmonics.

[0030] The voltage obtained through the voltage-tapped bushing is connected to the primary side of the step-down transformer of the electromagnetic voltage divider, and a capacitor bank Cb is connected in parallel on the secondary side for main voltage regulation. This capacitor bank also has a weak phase adjustment function and can be considered when specific phase accuracy requirements are required. The series circuit of inductor L and capacitor bank Cb is mainly used for phase adjustment of the circuit. By adjusting the switch of Cb, the phase change of the load output can be achieved within a large range. In addition, this capacitor switch also has a certain voltage regulation function. Voltage relays KV1, KV2, KV3, and KV4 are used for voltage monitoring. Among them, relay KV1 is used for transformer live measurement, with an activation range of 50% of the standard voltage, and outputs a switch signal. KV2 is used for undervoltage monitoring, selecting 90% of the standard voltage; if the voltage is below this range, a switch signal is output. KV3 is used for overvoltage monitoring; if the voltage exceeds 110%, KV3 outputs a switch signal. KV4 is used for overvoltage monitoring; if the voltage exceeds 120%, KV4 outputs a switch signal.

[0031] This invention utilizes the voltage division effect of the equivalent capacitances C1 and C2 of the high-voltage bushing to perform primary voltage proportional division on the high-voltage side, reducing the voltage output across C2 to a range that the high-voltage side of the voltage divider can withstand. The voltage divider uses its own configured Ca capacitor bank for switching operations, allowing the T1 transformer to output a voltage amplitude range close to the standard voltage output. Due to the inherent losses of T1 and T2, and the need for T2 to be connected to a small-power load, the output voltage and phase of T2 will change. By combining Cb and L1 and adjusting the capacitance value of Cb, the phase of the circuit can be shifted to synchronize with the phase of the power system voltage. When the adjustment range of Cb is limited, Cc can be used to compensate for the reactive current in the line, further expanding the phase change range, ultimately achieving a voltage and phase output that fully meets the voltage division ratio requirements. Voltage relays KV1 to KV4 are relays used to monitor system voltage fluctuations. They can be customized with new operating logic and voltage threshold adjustments according to user needs to provide monitoring of system voltage changes. Terminals 1 and 2 of terminal block P1 are used to measure the OUT1 voltage and can be used to monitor the OUT1 voltage output. Terminals 3 and 4 are used to measure the OUT2 output. Terminals 1-4 are mainly used to test whether the equipment is operating normally and can be used to measure the location of faults in sections. Terminals 5, 6, 7 and terminals 8, 9, 10 are the output terminals of the two independent output windings of the same T2 transformer. 5, 7 and 8, 10 are 110V outputs, and 6, 7 and 9, 10 are 63.5V outputs. Among them, S1-1 to S1-3 and S2-1 to S2-3 are single-phase miniature circuit breakers used to control the T2 output. They are manually operated and have an automatic short-circuit tripping function to protect the equipment from damage caused by short circuits. Terminals 11-18 are the signal terminals of voltage monitoring relays KV1 to KV4 and their switching signals KVS1 to KVS4. When the voltage changes to the corresponding set value, the voltage relay will output the corresponding switching signal to determine the alarm in four different states. After the capacitor bank adjustment is complete, the high-voltage input C1 in the entire system has a linear relationship with OUT2. Voltage monitoring primarily monitors the voltage at OUT2 to reflect changes in the proportional voltage input at C1. The logic definition of the voltage monitoring relay can be customized according to user requirements, and can be set to operate on undervoltage or overvoltage conditions. The parameters for determining the activation amount for undervoltage or overvoltage can be specified and set by the user.

[0032] In this invention, grounding switch Sg (serial number 4) is used for maintenance protection. When the equipment needs maintenance, Sg closes, bushing C2 is short-circuited, and all voltage from the high-voltage side is borne by C1. The subsequent circuits of this invention will have no external output due to the loss of voltage. At this time, the internal transformer T1, capacitors Ca and Cb, inductor L1, voltage monitoring relays KV1-KV4, transformer T2, and capacitor Cc will all lose voltage, allowing maintenance personnel to safely perform equipment maintenance activities.

[0033] R1 in this invention is a zinc oxide surge arrester, which is used to limit overvoltage caused when the grounding switch is opened.

[0034] The precision adjustment of this invention requires load matching. When a high-precision voltage output from the electromagnetic voltage divider is needed, the load must first be connected to the output terminal of the voltage divider, and a voltage monitoring device should be connected to the output terminal to monitor the output voltage and phase. Adjust capacitor Ca to first stabilize the voltage within the required output range. Then adjust capacitor Cb to make the phase of the output of T2 the same as the high-voltage side voltage of the system. If the phase adjustment exceeds the adjustment range of Cb, phase compensation can be performed by engaging capacitor Cc. The voltage amplitude after compensation will change, at which point Ca needs to be adjusted again to adjust the voltage amplitude. After repeating this process several times, the required output voltage and phase can be modulated. Once the output voltage stabilizes, the voltage divider output voltage and the high-voltage side voltage of the system will be output strictly proportionally.

[0035] This invention, through the combined action of Cb, L1, and Cc, can form a circuit up to the third order. Cb and L1 constitute a second-order bandpass filter circuit, effectively suppressing high-frequency and low-frequency components, ensuring the power supply waveform in the circuit is primarily controlled within its operating frequency range. Cc provides reactive power compensation to the load, indirectly forming a high-pass filter that bypasses the high-frequency components of the voltage divider from the bushing, reducing high-frequency interference from the connected load equipment.

Claims

1. A novel electromagnetic bushing voltage divider, characterized in that, include: The voltage input unit, step-down transformer T1, amplitude modulation and phase modulation unit, dual-winding output isolation transformer T2, and voltage output unit are connected in sequence. The secondary coil of the step-down transformer T1, the output terminal of the amplitude modulation and phase modulation unit, and the output terminal of the voltage output unit are respectively connected to different terminals on the terminal block P1. The amplitude and phase modulation unit includes: parallel capacitor bank Ca, parallel capacitor bank Cb, parallel capacitor bank Cc, phase-shifting inductor L1, and voltage monitoring relay group. The secondary coil a terminal of step-down transformer T1 is connected to the primary coil a terminal of dual-winding output isolation transformer T2 in sequence through parallel capacitor bank Cb and phase-shifting inductor L1. The secondary coil b terminal of step-down transformer T1 is connected to the primary coil b terminal of dual-winding output isolation transformer T2. The parallel capacitor bank Ca is connected in parallel across the two ends of the secondary coil of step-down transformer T1. The two ends of the primary coil of dual-winding output isolation transformer T2 are connected in parallel with the voltage monitoring relay group and the parallel capacitor bank Cc, respectively.

2. The novel electromagnetic bushing voltage divider according to claim 1, characterized in that, The voltage input unit includes: bushing equivalent high voltage capacitor C1, bushing equivalent low voltage capacitor C2, grounding switch Sg, and overvoltage protection surge arrester R1. The system voltage input terminal is grounded in sequence through the bushing equivalent high voltage capacitor C1 and the bushing equivalent low voltage capacitor C2. The bushing equivalent low voltage capacitor C2, grounding switch Sg, and overvoltage protection surge arrester R1 are connected in parallel with the primary coil of step-down transformer T1.

3. The novel electromagnetic bushing voltage divider according to claim 1, characterized in that, The parallel capacitor bank Ca, parallel capacitor bank Cb and parallel capacitor bank Cc are each composed of multiple parallel branches, and each branch consists of a switching switch and a capacitor connected in sequence.

4. The novel electromagnetic bushing voltage divider according to claim 1, characterized in that, The voltage monitoring relay group consists of four voltage monitoring relays KV1-KV4. The two ends of the coil of each voltage monitoring relay are connected in parallel with the primary coil of the dual-winding output isolation transformer T2. The contacts of each voltage monitoring relay are used to send a switching signal.

5. A novel electromagnetic bushing voltage divider according to claim 1, characterized in that, The voltage output unit consists of two sets of switch groups, each set of switch groups consists of three branches, and each branch has one switch. In the first set of switch groups, one end of each branch is connected to a contact of the primary winding of the dual-winding output isolation transformer T2, and the other end of the three branches is connected to different terminals on the terminal block P1. In the second set of switch groups, one end of each branch is connected to a contact of the primary winding of the dual-winding output isolation transformer T2, and the other end of the three branches is connected to different terminals on the terminal block P1.

6. A novel electromagnetic bushing voltage divider according to claim 1, characterized in that, The terminal connected to the secondary coil of the step-down transformer T1 is used to output the voltage OUT1 after being stepped down by the step-down transformer T1; the terminal connected to the output terminal of the amplitude modulation and phase modulation unit is used to output the voltage OUT2 after being processed by the amplitude modulation and phase modulation unit; the terminal connected to the output terminal of the voltage output unit is used to output two independent voltages, namely AC110V and AC63.5V, after being stepped down by the dual-winding output isolation transformer T2.

7. The voltage dividing method of a novel electromagnetic bushing voltage divider according to claim 1, characterized in that, The voltage from the bushing voltage tap is linearly stepped down to between AC 90V and 200V via the voltage input unit and step-down transformer T1. The amplitudes of the secondary output voltages OUT1 and OUT2 are adjusted by switching on the parallel capacitor bank Ca. The phases of the secondary output voltages OUT1 and OUT2 are adjusted by switching on the parallel capacitor bank Cb. The amplitudes and phases of the adjusted voltages OUT1 and OUT2 are balanced by switching on the parallel capacitor bank Cc. The voltage is filtered by increasing the capacitance of the parallel capacitor bank Cc. The dual-winding output isolation transformer T2 outputs the filtered voltage as two independent voltages, namely AC 110V and AC 63.5V.

8. The voltage dividing method of a novel electromagnetic bushing voltage divider according to claim 7, characterized in that, The voltage in the voltage divider is monitored by a group of voltage monitoring relays. Specifically, voltage monitoring relay KV1 is used for transformer live measurement; it activates and outputs a switching signal when the voltage in the voltage divider exceeds 50% of the standard voltage. Voltage monitoring relay KV2 is used for undervoltage monitoring; it activates and outputs a switching signal when the voltage in the voltage divider falls below 90% of the standard voltage. Voltage monitoring relay KV3 is used for overvoltage monitoring; it activates and outputs a switching signal when the voltage in the voltage divider exceeds 110% of the standard voltage. Voltage monitoring relay KV4 is used for overvoltage monitoring; it activates and outputs a switching signal when the voltage in the voltage divider exceeds 120% of the standard voltage.

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