Electrician Red Seal · Question
A delta-connected primary of a 600 V / 208 Y / 120 V transformer bank is composed of three single-phase transformers. If one transformer fails and the bank is to be operated in an open-delta configuration, what percentage of the original three-phase kVA capacity is retained, assuming the remaining transformers are not overloaded?
When a three-phase delta-connected transformer bank loses one transformer and operates in open delta (V-V connection), the available three-phase kVA capacity is
Start free practice for Electrician Red Seal
150 questions · no signup required · 40 free questions per day
Question: A delta-connected primary of a 600 V / 208 Y / 120 V transformer bank is composed of three single-phase transformers. If one transformer fails and the bank is to be operated in an open-delta configuration, what percentage of the original three-phase kVA capacity is retained, assuming the remaining transformers are not overloaded?
Answer options:
- 33.3% ✅ 57.7%
- 66.7%
- 86.6%
Correct answer: 57.7%
Explanation: When a three-phase delta-connected transformer bank loses one transformer and operates in open delta (V-V connection), the available three-phase kVA capacity is reduced to 57.7% (or 1/√3) of the original three-phase kVA rating. Each of the remaining two transformers is loaded to 86.6% of its rating to deliver 57.7% of the total capacity.
Start free practice for Electrician Red Seal
150 questions · no signup required · 40 free questions per day
More about Electrician Red Seal
Related Questions
- A residential garage is to be wired with a 15 A, 120 V duplex receptacle. According to the Canadian Electrical
- During a renovation of a commercial kitchen, an electrician needs to replace an old single-phase, 240 V, 5 kW
- A commercial kitchen is being renovated, and several new 4 kW, 208 V, single-phase electric ovens are being in
- What is the minimum working space depth required in front of an electrical panel rated 200 A, 120/240 V, locat
- A Red Seal electrician is setting up temporary power for a construction site. The main temporary service is a
- A new industrial facility requires a 600 V, three-phase, 150 A feeder to supply a motor control centre. The co
More for Electrician Red Seal candidates
Practice tests
Question explanations
- A residential garage is to be wired with a 15 A, 120 V duplex receptacle. According to the Canadian Electrical
- During a renovation of a commercial kitchen, an electrician needs to replace an old single-phase, 240 V, 5 kW
- A commercial kitchen is being renovated, and several new 4 kW, 208 V, single-phase electric ovens are being in
- What is the minimum working space depth required in front of an electrical panel rated 200 A, 120/240 V, locat
Ready to practice?
Free, no signup required. Build a wrong-question list as you go.
Start Free Electrician Red Seal Practice →Related courses
Other Canadian certifications candidates often prepare for alongside this one.