Variable Frequency Power System

The PD free variable frequency power supply can be used for AC withstａnd voltage test and partial discharge test of all electrical equipment. The excitation transformer is used to excite the series or parallel resonant circuit. By adjusting the output frequency of the variable frequency power supply, the reactor inductance L and the sample capacitor C in the circuit resonate, and the resonance voltage is the voltage applied to the sample. Or directly output to the transformer primary through an intermediate transformer for inductive withstａnd voltage test.

HMCHXB-15 PD free variable frequency power supply is the main component of the complete test system, which is suitable for:

·Induction withstａnd voltage and partial discharge test of power transformer.

·AC withstａnd voltage and partial discharge tests of transformers, etc.

·AC withstａnd voltage test of power cable.

·GIS combined electrical AC withstａnd voltage test.

·AC withstａnd voltage test of capacitive equipment such as circuit breakers, isolating switches, insulators, bushings, etc.

·It is suitable for power frequency withstａnd voltage test of large generator set.

·Suitable for power supply for large-scale ground network testing.

·Rated input voltage: three-phase AC 380V±10%, 50Hz

·Rated output power: single-phase 15kW

·Output frequency range: 30Hz～300Hz, continuously adjustable

·Rated output voltage: 0～350V, continuously adjustable

·Rated output current: 0～42.8A, continuously adjustable

·Frequency instability: ≤0.05%

·Voltage instability: ≤1.0%

·Non-linear distortion: ≤1%

·Partial discharge capacity: ≤10pC (measured at the high voltage side of the booster)

·Working conditions: temperature -10℃～＋45℃, humidity: 10-90%RH, altitude: ≤1000 meters

·Cooling method: forced air cooling

·The altitude does not exceed 1000m

·Temperature -20℃～+45℃, relative humidity is not more than 90% (at 20℃), the temperature difference from one environment to another is not more than 25℃

·No conductive dust

·No fire and explosion hazard

·Does not contain gases and vapors that corrode metals and insulation

·No severe collision and strong turbulence

·Wind speed＜12m/s

·A reliable grounding point is provided, and the power supply side should not suffer from external overvoltage

The equivalence of the test is good. The output of this device is a sine wave with low waveform distortion. Waveform distortion rate <3%, which is different from other types of variable frequency power supply devices (other types of variable frequency power supply devices are square wave output, sine waves formed after waveform shaping). Therefore, the device does not need to measure the peak value during the test.

·It adopts optical fiber control to completely isolate the high-voltage and low-voltage control loops.

Small size, light weight, flexible handling, very suitable for on-site use.

·The operation is simple and convenient, the wiring is simple, and the work efficiency can be improved by 50% (compared to the generator set method).

·Safe and reliable, a variety of protections are integrated in this device. Including: discharge breakdown protection, overvoltage setting protection, output short circuit protection, boot zero protection, bridge arm amplifier circuit protection, power curve protection, etc. When any kind of protection appears, the device immediately cuts off the test voltage output and cut off the main circuit power supply to ensure the safety of the test personnel, the tested product and the test system.

·The signal source in this device is generated by a dedicated chip and controlled by a microcomputer. The output frequency is stable and can reach 0.01Hz.

·The variable frequency output voltage is controlled by TI's high-speed microcomputer, and the instability of the output voltage is less than 1%.

The high-power output of the variable frequency power supply device adopts the principle of stepwise amplification. From the original small power signal source, after many times of amplification, high-power output is achieved, which meets the needs of the test.

The signal source uses a variable frequency function generator to generate a standard sine wave signal through a digital potentiometer for voltage adjustment. This process is also the frequency adjustment and voltage adjustment during the test. The frequency at this time is the same as the test frequency, and the adjustment of frequency and voltage is realized in the signal source part. The output of the signal source directly drives the "pre-amplifier", which has a preliminary power output. This "pre-amplifier" is divided into two channels, one of which generates a "synchronous power supply" with the same test frequency and supplies it to the partial amplifier; the other is used To promote the "bridge power amplifier circuit." "Bridge power amplifier circuit" is the main part of high-power generation. During the test, it generates a lot of heat and requires an air-cooled system to dissipate heat.

The four equivalent triodes correspond to the four bridge arms of the variable frequency power supply. Each bridge arm is composed of thousands of transistors in parallel, and effective current sharing measures are taken. In the positive half cycle, the preamplified signal acts on the base of the transistors Q1 to Q4 through the driving transformer (T1 to T4), Q2 and Q3 are cut off; Q1 and Q4 are on, and the current flows from Q1 to the load and then to Q4 to form a positive sine wave. Half a week. In the negative half cycle, the analog signal pushes the base of Q2 and Q3, Q1 and Q4 are cut off, Q2 and Q3 are turned on, and the current flows from Q3 to the load and then to Q2 to form the negative half cycle of the sine wave, thus forming a complete sine wave on the load.

"Bridge power amplifier circuit" also needs a high-power DC power supply as a working power supply. The power supply of this device is directly taken from a three-phase 380V AC power supply, and sent to a three-phase bridge rectifier circuit through a vacuum switch with overcurrent and quick-break protection, and it becomes a pulsating DC, which is converted to a pulsating DC by a filter circuit composed of a filter inductance and a filter capacitor. It becomes a smooth DC power supply "bridge power amplifier circuit". Since the capacitance of the filter capacitor reaches tens of thousands of microfarads, it is directly closed and the charging current is very large, which may cause the main power switch to trip. Therefore, a pre-closing circuit is added to the device. The filter capacitor is charged with a small current first, and then closed when the capacitor charging current is small, without a large starting inrush current. After the switch is opened, the stored charge on the filter capacitor is slowly released through the discharge resistor. When this device is used, the fan startup, pre-closing, and closing processes are all automatically completed, and no step-by-step operation is required (just press the "start" button of the control box).

The entire device protection circuit is controlled by the "fast overcurrent protection" part of the DC working power supply of the "bridge amplifier circuit". When a fault occurs, the working power supply is quickly cut off to protect the subsequent circuit.

The output terminals (OUT1, OUT2) of the "bridge power amplifier circuit" are connected to the low-voltage end of the intermediate step-up transformer, and the high-voltage end of the intermediate step-up transformer is connected to the test circuit. There is no open circuit in the test circuit and the intermediate step-up transformer, and there is always an energy release channel. It can be seen that regardless of the internal failure of the variable frequency power supply or the sudden power failure of the external power supply, the tested transformer or resonant circuit is not cut off. It is completely different from the traditional test transformer. There is no forced current to cross zero, and the device will not generate overvoltage.