Basic information of users
A gate valve casting company mainly produces valve products. The company’s production line equipment includes a set of 2-ton medium-frequency induction furnace, which is powered by a 2000 kVA (10KV/0.75 kVA) professional transformer power supply system. Equipped with 2 capacitance compensation cabinets with a volume of 600 kVA, a 1-ton intermediate frequency induction furnace, 800 kVA (10KV/0.4KV) technical and professional transformers, and a capacitance compensation cabinet with a volume of 300 kVA . The power supply system diagram is as follows:
Actual operating data
The apparent power of the intermediate frequency induction furnace equipped with a 2000KVA transformer is 700KVA-2100KVA, the active power is P=280KW-1930KW, the reactive load is Q=687KAR-830KAR, the power factor is PF=0.4-0.92, and the current in operationⅰ = 538 A-1660 A, the apparent power of the intermediate frequency induction furnace equipped with 800KVA transformer is 200KVA-836KVA. The active power is P=60KW-750KW, the reactive load is Q=190KAR-360KAR, the power factor is PF=0.3-0.9, and the working current i=288 A-1200 A. Because the capacitor compensation cabinet cannot be put into operation (automatic compensation fails, when the capacitor is manually put into use, the capacitor noise is abnormal, the circuit breaker trips, the capacitor is packaged, oil leaked, cracked, and cannot be used), the monthly comprehensive power The factor is PF=0.78, and the monthly mortgage interest rate is adjusted to more than 32,000 yuan.
Power System Situation Analysis
The main load of the intermediate frequency electric furnace rectifier power supply is 6-pulse rectification. The rectifier equipment converts AC into DC while generating a large number of harmonics. The typical harmonic source harmonic current is injected into the grid, and the impedance of the grid generates harmonic voltage, causing grid voltage Current distortion affects the quality of power supply and operation safety, increases line loss and voltage offset, and increases power. When the reactive power compensation capacitor bank is put into operation, because the harmonic characteristic impedance of the capacitor bank is small, many harmonics are introduced into the capacitor bank, and the amount of capacitive current The rapid increase seriously affects its service life. On the other hand, when the harmonic capacitive reactance of the capacitor bank is equal to the equivalent harmonic inductive reactance of the system and a series resonance occurs, the harmonic current is seriously enlarged (2-10 times), resulting in overheating and damage to the capacitor. In addition, the harmonics will cause the DC sinusoidal wave to change, resulting in a sawtooth peak wave, which is easy to cause partial discharge in the insulating material. Long-term partial discharge will also accelerate the aging of the insulating material and easily cause capacitor damage. Therefore, the capacitor reactive power compensation cabinet cannot be used for the compensation of the intermediate frequency induction furnace, and a filter reactive power compensation device with pulse current suppression function should be selected.
Reactive power compensation treatment plan
Governance goals
The design of filter compensation equipment meets the requirements of harmonic suppression and reactive power suppression management.
Under the operating mode of 0.75KV and 0.4KV systems, after the filter compensation equipment is put into operation, the pulse current is suppressed, and the monthly average power factor exceeds 0.95. The input of the filter compensation loop will not cause pulse current resonance or resonance overvoltage and overcurrent.
Design Follows Standards
Power quality Public grid harmonics GB/T14519-1993
Power quality Voltage fluctuation and flicker GB12326-2000
General technical conditions of low-voltage reactive power compensation device GB/T 15576-1995
Low-voltage reactive power compensation device JB/T 7115-1993
Reactive power compensation technical conditions; JB/T9663-1999 “Low-voltage reactive power automatic compensation controller”
Limits of harmonic current emitted by low-voltage electrical and electronic equipment GB/T 17625.7-1998 Electrotechnical terms Power capacitors GB/T 2900.16-1996
Low voltage shunt capacitor GB/T 3983.1-1989
Reactor GB10229-88
Reactor IEC 289-88
Low-voltage reactive power compensation controller order technical conditions DL/T597-1996
Low-voltage electrical enclosure protection grade GB5013.1-1997
Low-voltage complete switchgear and control equipment GB7251.1-1997
Design ideas
According to the specific situation of the company, our company has designed a set of detailed intermediate frequency induction furnace reactive power compensation filter scheme. Fully consider the load power factor and harmonic suppression, and install a set of low-voltage reactive power compensation filters on the bottom voltage side of the company’s 0.75KV and 0.4KV transformers to suppress harmonics, compensate reactive power, and improve power factor. During the operation of the intermediate frequency furnace, the rectifier device generates 6K+1 harmonics, and the Fourier series is used to decompose and transform the current to generate 5 harmonics of 250HZ and 7 harmonics above 350HZ. Therefore, when designing the filter ineffective compensation of the frequency furnace, it should be ensured that the filter compensation branch circuit compensates for the inactive power by effectively suppressing the harmonics of frequencies above 250HZ and 350HZ, and increases the power factor.
design assignment
The comprehensive power factor of the 2-ton intermediate frequency induction furnace matched with the 2000 kVA transformer is compensated from 0.78 to about 0.95. The filter compensation device needs to be equipped with a capacity of 820 kVA, and automatically converts into 6 groups of capacities, each of which matches the winding on the bottom voltage side of the transformer for compensation. The grade classification adjustment capacity is 60KVAR, which can meet various power requirements of the medium frequency induction furnace. The comprehensive power factor of the 1 ton intermediate frequency induction furnace matched with the 800 kVA transformer is compensated from 0.78 to about 0.95. The filter compensation equipment needs to be equipped with a capacity of 360 kVA, which can be automatically converted into 6 groups of capacity, and the graded adjustment capacity is 50 kVA, which can meet various power requirements of the intermediate frequency induction furnace. This type of design fully guarantees that the adjusted power factor is higher than 0.95.
Effect analysis after installation of filter compensation
At the beginning of June 2010, the intermediate frequency furnace filter reactive power compensation device was installed and put into operation. The equipment automatically tracks the load change of the intermediate frequency induction furnace, specifically compensates the reactive load, and improves the power factor. details as following:
Post time: Apr-14-2023