Question 1

Which factory acceptance and inspection arrangement should we choose for our transformer order?

Accepted Answer

For a critical or customized project, the recommended order is: 1) all required tests plus an approved customer or third-party witness and document-review plan; 2) manufacturer tes…

Question 2

Which transformer impedance should we select for our project?

Accepted Answer

The recommended order is: 1) the impedance approved by the fault-level, voltage-performance and protection studies; 2) an alternative value only after those studies are updated and…

Question 3

Should we choose Dyn11 or Yyn0 for our distribution transformer?

Accepted Answer

For an existing installation, the recommended order is: 1) the vector group required by the approved system design and existing equipment; 2) an alternative only after engineering …

Question 4

Should we install one large transformer or two smaller transformers?

Accepted Answer

For a project that must maintain specified critical loads during a transformer outage, the recommended order is: 1) a properly engineered two-transformer arrangement with adequate …

Question 5

What transformer capacity should we choose for our project?

Accepted Answer

The recommended order is: 1) a standard rating that meets the verified maximum demand, starting requirements and confirmed expansion plan; 2) a larger rating where its additional c…

Question 6

Should we choose mineral oil or an ester insulating fluid for our transformer?

Accepted Answer

For a new liquid-filled transformer where fire-risk reduction and environmental performance are priorities, the suggested order is: a transformer designed for an approved ester flu…

Question 7

Should we choose a hermetically sealed transformer or a conservator-type transformer?

Accepted Answer

For a distribution application where an approved sealed design is available and limited routine attention is a priority, the suggested order is: 1) hermetically sealed design; 2) c…

Question 8

Should we choose a compact substation or install the transformer and switchgear separately?

Accepted Answer

For a project with limited space, defined interfaces and a need to reduce site assembly, the suggested order is: 1) a suitable factory-integrated compact substation; 2) separately …

Question 9

Is a lower-loss transformer worth the higher purchase price?

Accepted Answer

For a continuously energized project with a long service horizon, the suggested order is: 1) a compliant design with the lowest evaluated lifecycle cost; 2) a lower-price design if…

Question 10

Should we choose an ONAN transformer or an ONAN/ONAF transformer?

Accepted Answer

For a project that must carry its required load without relying on fans, the suggested order is: 1) ONAN rated for that load; 2) ONAN/ONAF with an adequate ONAN base rating. For a …

Question 11

Should our transformer use an OLTC or a de-energized tap changer?

Accepted Answer

Where voltage adjustment is required during normal operation without interrupting supply, the suggested order is: 1) OLTC with suitable voltage-regulation controls; 2) DETC/OCTC on…

Question 12

Should we choose copper or aluminium windings for our transformer?

Accepted Answer

For a replacement project with tight dimensional limits, the suggested comparison order is: 1) a compliant copper-wound design; 2) a compliant aluminium-wound design that fits the …

Question 13

Which transformer should we choose for our project: dry-type or liquid-immersed?

Accepted Answer

For an indoor project where fire safety and avoiding insulating liquid are the main priorities, the suggested order is: 1) dry-type transformer; 2) an approved less-flammable liqui…

Question 14

What is transformer short-circuit impedance?

Accepted Answer

Short-circuit impedance is the equivalent series impedance between a pair of transformer windings at specified frequency, temperature and tap position. It is commonly specified as …

Question 15

What is the difference between single-phase and three-phase transformers?

Accepted Answer

The number of phases describes the AC system arrangement for which a transformer is designed. Single-phase transformers serve single-phase circuits, while three-phase transformers …

Question 16

What is transformer rated frequency?

Accepted Answer

Rated frequency is the AC supply frequency for which a transformer is designed and rated. A conventional transformer changes voltage but does not change frequency. Operation at a d…

Question 17

What is a transformer winding, and how does the winding material affect performance?

Accepted Answer

A transformer winding is an assembly of insulated conductors that carries current and interacts with the changing magnetic flux to transfer electrical energy. Copper and aluminium …

Question 18

What is transformer temperature rise?

Accepted Answer

Temperature rise is the increase in transformer oil, winding or other component temperature above the surrounding ambient temperature under specified operating conditions.

Question 19

What is transformer cooling method?

Accepted Answer

Transformer cooling method describes how heat is removed from the transformer core and windings. It directly affects permissible loading, temperature rise, equipment configuration …

Question 20

What is transformer load loss?

Accepted Answer

Load loss is the power loss caused mainly by winding resistance and stray losses when current flows through a loaded transformer. It increases significantly as load current increas…

Question 21

What is transformer no-load loss?

Accepted Answer

No-load loss is the power consumed mainly by the transformer core whenever the transformer is energized, even if no customer load is connected to the secondary side.

Question 22

What is the difference between OLTC, DETC and OCTC?

Accepted Answer

A tap changer adjusts the effective winding turns ratio to regulate voltage. OLTC can change taps under load, while DETC and OCTC normally require the transformer to be isolated an…

Question 23

What is the relationship between insulation level and BIL?

Accepted Answer

Insulation level is the complete withstand capability of the transformer insulation system. BIL, or Basic Lightning Impulse Level, is one important part of the insulation level and…

Question 24

What is transformer impedance or Uk%?

Accepted Answer

Transformer impedance, usually expressed as Uk% or percentage impedance, affects fault current, voltage regulation, protection coordination and load sharing during parallel operati…

Question 25

What is a transformer vector group?

Accepted Answer

A vector group defines the winding connection method, phase displacement and neutral availability of a transformer. It affects grounding, protection, harmonics and parallel-operati…

Question 26

What is a transformer voltage ratio?

Accepted Answer

The voltage ratio is the rated relationship between the transformer primary and secondary voltages. It determines whether the transformer steps voltage up or steps voltage down for…

Question 27

What is the rated capacity of a transformer?

Accepted Answer

Rated capacity is the apparent power that a transformer can continuously deliver under specified voltage, frequency, cooling and temperature-rise conditions. It is normally express…

Question 28

What is transformer inrush current?

Accepted Answer

Transformer inrush current is a temporary high magnetizing current that may occur during energization because of core saturation, switching angle and residual magnetic flux. It is …

Question 29

What is the difference between OLTC, DETC and OCTC?

Accepted Answer

Tap changers adjust the effective turns ratio to control voltage. OLTC can change taps under load; DETC and OCTC normally require the transformer to be de-energized before operatio…

Question 30

What is the difference between ONAN and ONAF cooling?

Accepted Answer

ONAN uses natural oil circulation and natural air cooling. ONAF uses natural oil circulation with forced air from fans. ONAF operation can provide a higher approved rating only whe…

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FAQ e Respostas de Conhecimento

Perguntas e respostas

Which factory acceptance and inspection arrangement should we choose for our transformer order?

Tem um requisito de projeto?