Basic information of users
A gate valve casting company mainly produces valve products. The company’s production line equipment includes a one-ton medium-frequency induction furnace, which uses a 2000 kVA (10KV/0.75 kVA) technical professional transformer power supply system, and is equipped with two capacitor compensation cabinets with a volume of 600 kVA, a one-ton medium-frequency induction furnace, 800 kVA (10KV/0.4 kVA) technical professional transformer power supply system, a capacitor compensation cabinet with a volume of 300 kVA. The power supply system diagram is as follows:
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 key load of rectified power supply for medium frequency induction furnace is six single pulse ballasts. The rectifier equipment produces a lot of harmonics when it converts AC current to DC, which is a typical source of harmonics. The harmonic current introduced into the power grid will cause harmonic working voltage on the characteristic impedance of the power grid, resulting in frame loss of the working voltage and current of the power grid, endangering the quality and operation safety of the power supply system, increasing the line loss and working voltage deviation, and causing damage to the power grid and processing The factory’s own electrical equipment will cause adverse hazards. When the reactive power compensation capacitor bank is put into operation, because the harmonic characteristic impedance of the capacitor bank is small, a large number of harmonics are introduced into the capacitor bank, and the capacitance current increases rapidly, seriously affecting 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
Filter compensation devices are designed to meet regulatory requirements for suppression of harmonics and reactive power.
In the operation mode of 0.75KV and 0.4KV systems, after the filter compensation equipment leaves the factory, the high-order harmonics are suppressed at a monthly average power factor of 0.95 or more.
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” Harmonic current limit value of 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, in the design of intermediate frequency induction furnace filter reactive power compensation, the frequency of 250HZ, 350HZ and around must be designed to ensure that the filter compensation loop can reasonably suppress the pulse current while compensating the reactive load and improving 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:
After the filter compensation device is switched on, the power factor change curve is about 0.97 (the power factor when the filter compensation device is cut off is about 0.8)
Load operation
The current of the 2000KVA transformer is reduced from 1530A to 1210A, a decrease of 21%; the current of an 800KVA transformer is reduced from 1140A to 920A, a decrease of 19.3%, which is equal to a 20% reduction of the transformer, that is, 560KVA, and the output power damage after compensation is reduced by 21%. ; Transformer damage reduced by WT=?Pd1S2) 2**[1-(1-1/cos2)2]=24{(0.78?2800)/280}20.415(kwh). The transformer loss is 24 yuan, and the monthly loss is 15KW=150d; the monthly saving cost is 1580d=230d*30d(2307){0.782800}20d.
power factor situation
This month, the company’s comprehensive power factor increased from 0.78 to 0.97, the monthly reactive rate and utility bills were adjusted to 0, and the penalty was changed to 4,680 yuan. Since then, the monthly power factor has remained at 0.97-0.98, and the monthly reward has been between 3,000-5,000 yuan.
In general, this product has excellent ability to suppress pulse current and compensate reactive power, solve the company’s long-term problem of bearing interest rate and utility fee penalties, improve the output capacity of transformers, and bring obvious economic benefits to the company , Recovered the customer’s investment in less than a year. Therefore, the reactive power compensation of the intermediate frequency furnace manufactured by the company is very satisfactory, and will attract many customers in the future.
Post time: Apr-14-2023