Machine Parts

This is an excellent application for air cooled transformers. Even though the inrush or starting current is five to seven times normal running current the resultant lower voltage caused by this momentary overloading is actually beneficial in that a cushioning effect on motor starting is the result. The tables shown in "Steps for Selecting a Transformer" illustrate some typical requirements for use with motor applications. 

A transformer will not act as a phase changing device when attempting to change three phase to single phase. There is no way that a transformer will take three phase in and deliver single phase out while at the same time presenting a balanced load to the three phase supply system. There are, however, circuits available to change three phase to two phase or vice versa using standard dual wound transformers. Please contact the factory for two phase applications. 

Exciting current, when used in connection with transformers, is the current or amperes required for excitation. The exciting current on most fighting and power transformers varies from approximately 10% on small sizes of about 1 KVA and smaller to approximately .5% to 4% on larger sizes of 750 KVA. The exciting current is made up of two components, one of which is a real component and is in the form of losses or referred to as no load watts; the other is in the form of reactive power and is referred to as KVAR. 

Polarity is the instantaneous voltage obtained from the primary winding in relation to the secondary winding. Transformers 600 volts and below are normally connected in additive polarity - that is, when tested the terminals of the high voltage and low voltage windings on the left hand side are connected together, refer to diagram below. This leaves one high voltage and one low voltage terminal unconnected. When the transformer is excited, the resultant voltage appearing across a voltmeter will be the sum of the high and low voltage windings. This is useful when connecting single phase transformers in parallel for three phase operations. Polarity is a term used only with single phase transformers. 

BIL is an abbreviation for Basic Impulse Level. Impulse tests are dielectric tests that consist of the application of a high frequency steep wave front voltage between windings, and between windings and ground. The Basic Impulse Level of a transformer is a method of expressing the voltage surge lightning, sw itching surges, etc.) that a transformer will tolerate without breakdown. A ll transformers manufactured in this catalog, 600 volts and below, will withstand the NEMA standard BIL rating, which is 10 KV. This assures the user that he will not experience breakdowns when his system is properly protected with lightning arrestors or similar surge protection devices. 

Most ACME transformers shown in this catalog are certified by Canadian Standards Association. They have been designed and tested in accordance with the latest specifications. Please contact the factory if further details are required. 

All of the transformers, with few exceptions, are listed by Underwriters' Laboratories and have met their rigorous requirements. We are also prepared to have transformers, which are not presently listed, submitted for listing to Underwriters' upon the customer's request. Please contact the factory for details. 

Several standard single phase transformers listed in this catalog can be connected as auto transformers. The KVA capacity will be greatly increased when used as an auto transformer, in comparison to the nameplate KVA as an insulating transformer.  E xamples of auto transformer applications are changing 600 volts to 480 volts in either single phase or three phase; changing 480 volts to 240 volts single or three phase or vice versa; or the developing of a fourth wire (neutral) from a 480 volt three phase three wire system for obtaining 277 volts single phase. Th is voltage is normally used for operating fluorescent lamps or similar devices requiring 277 volts. For further details showing KVA and voltage combinations for various auto transformer connections refer to the Acme catalog.

When the ambient exceeds 40 deg. C use the following chart for de-rating standard transformers.      Maximum Ambient Temperature    Maximum Percentage of Loading 40 deg. C (104 deg. F )                                   100% 50 deg. C (122 deg. F)                                    92% 60 deg. C (140 deg. F)                                    84% Instead of ordering custom built transformers to operate in ambients higher than 40 deg.  C, it is more economical to use a standard transformer of a larger KVA rating.

ASA 61 (NEMA) light gray is used on all enclosed transformers from .050 to 500 KVA.