At a large chemical plant in an industrial area, electricity is the heart of production. The distillation process, chemical pumps, heating reactors—none of them can stop, not even for a second.
At the main distribution center, a 10,000 kVA transformer converts the voltage from 20,000 volts to 3,300 volts to supply various critical loads.
The plant's electrical team realized one crucial thing:
The VCB(VACUUM CIRCUIT BREAKER) installed on the secondary side of this transformer must be selected correctly.
Because one mistake could result in a shutdown, resulting in millions of dollar in losses.
Why is a VCB Important in a Chemical Plant?
A chemical plant is not like a typical factory. Because the electrical system is used:
- Providing power to large motors (pumps, compressors, mixers)
- Driving HVAC systems for chemical temperature control
- Powering highly sensitive control and instrumentation systems
Finding the Right VCB Guard
Technical data for the transformer obtained:
- Capacity: 10,000 kVA
- Primary voltage: 20,000 V
- Secondary voltage: 3,300 V
- Transformer impedance: 8%
Step 1 – Calculate the nominal secondary current:
Inominal = 1750 A
Step 2 – Calculate the short-circuit current:
sc = ZInominal = 21.875 A = 21.9 kA.
The VCB must be able to interrupt currents up to 22 kA, with a safety margin. Therefore, a minimum capacity of 25 kA is recommended, or a larger capacity can be used.
Based on the calculations above, the selected VCB must be capable of:
- Transmitting currents of ≥ 2000 A
- Breaking short-circuit currents of ≥ 25 kA
- Operating in 3.6/7.2 kV systems
- Complying with IEC 62271-100/JIS/the applicable standard
The main, but not limited, criteria for selecting a Vacuum Circuit Breaker (VCB), especially for medium-voltage systems such as 3.3 kV transformers:
1. Rated Voltage
2. Rated Current
3. Breaking Capacity / Short-Circuit Current Rating
4. Operating Frequency
5. Operating Mechanism
6. Operational Durability
7. Used Standards and Certifications
8. Additional Accessories (Optional but important)
Kingrun Transformer Instrument Co.,Ltd.
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