Machine Parts

ACME transformers should be specified to: 1.Distribute power at high voltage.   2.Eliminate double wiring. 3.Operate 120 volt equipment from power circuits. 4.Insulate circuits/establish separately derived circuits. 5.Provide 3-wire secondary circuits.   6.Buck and Boost 7.Provide electrostatic shielding transient noise protection.

Each phase of a three phase transformer must be considered as a single phase transformer when determining loading. For example: A 45 KVA three phase transformer with a 208Y/120 volt secondary is to service 4 loads at 120 volts single phase each. These loads are 10 KVA, 5 KVA, 8 KVA, and 4 KVA. That maximum loading on any phase does not exceed 10 KVA. Each phase has a 15 KVA capacity.  45 KVA = 15 KVA per phase         _____        3 phase  If incorrect method is used, phase B will have an 18 KVA load which is 3 KVA above its normal capacity of 15 KVA and failure will result even though we only have a total load of 27 KVA on a 45 KVA transformer. 

Yes. There are occasions where 480 volts single phase can be stepped down to 240 volts single phase by autoconnecting a standard. If connected in this manner, the nameplate KVA is doubled.

Industrial control equipment demands a momentary overload capacity of three to eight times normal capacity. This is most prevalent in solenoid or magnetic contactor applications where inrush currents can be three to eight times as high as normal sealed or holding currents but still maintain normal voltage at this momentary overloaded condition. Distribution transformers are designed for good regulation up to 100 percent loading, but their output voltage will drop rapidly on momentary overloads of this type making them unsuitable for high inrush applications. Industrial control transformers are designed especially for maintaining a high degree of regulation even at eight times normal load. This results in a larger and generally more expensive transformer. For a complete listing of ACME industrial control transformers, refer to Section V in the ACME catalog. 

The minimum transformer KVA rating required to operate a motor is calculated as follows:  Minimum Transformer KVA  Running Load Amperes x 1.73 x Motor Operating Voltage _____________________________________________________                                          1000  NOTE: If motor is to be started more than once per hour add 20% additional KVA.  Care should be exercised in sizing a transformer for an induction type squirrel cage motor as when it is started, the lock rotor amperage is approximately 5 to 7 times the running load amperage. This severe starting overload will result in a drop of the transformer output voltage. When the voltage is low the torque and the horsepower of the motor will drop proportionately to the square of the voltage. For example: If the voltage were to drop to 70% of nominal, then motor horse power and torque would drop to 70% squared or 49% of the motor nameplate rating. The underlying problem is low voltage at the moto

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.

Yes. This system can be used for either grounding or developing a fourth wire  from a three phase neutral. An example would be to change a 480 V - three  phase - three wire system to a 480Y/277 V - three phase - four wire system.

Yes. Three phase transformers are sometimesnot readily available whereas single phase transformers can generally be found in stock. Three single phase transformers can be used in delta connected primary and wye or delta connected secondary. They should never be connected wye primary to wye secondary, since this will result in unstable secondary voltage. The equivalent three phase capacity when properly connected of three single phase transformers is three times the nameplate rating of each single phase transformer. For example: Three 10 KVA single phase transformers will accommodate a 30 KVA three phase load.

It is used for determining the interrupting capacity of a circuit breaker or fuse employed to protect the primary of a transformer. Example : Determine a minimum circuit breaker trip rating and interrupting capacity for a 10 KVA single phase transformer with 4% impedance, to be operated from a 480 volt 60 Hz source. Calculate as follows: Normal Full Load Current = Nameplate Volt Amps 10,000 VA __________________ = __________ =                             Line Volts 480 V                                                           20.8 Amperes Maximum Short Circuit Amps = Full Load Amps 20.8 Amps _____________ = _________ =      4%                           4% 520 Amps The breaker or fuse would have a minimum interrupting rating of 520 amps at 480 volts. Example: Determine the interrupting capacity, in amperes, of a circuit breaker or fuse required for a 75 KVA, three phase transformer, wit

Impedance is the current limiting characteristic of a transformer and is expressed in percentage.

No. This can be compared with an ordinary light bulb. The filament temperature of a light bulb can exceed 2000 degrees, yet the surface temperature of the bulb is low enough to permit touching with bare hands. 

Not necessarily. It depends on the application and the cost benefit to be realized. Higher temperature class insulation systems cost more and larger transformers are more expensive to build. Therefore, the more expensive insulation systems are more likely to be found in the larger KVA units. All of these insulation systems will normally have the same number of years operating life. A well designed transformer, observing these temperature limits, will have a life expectancy of 20-25 years. 

Insulation class was the original method used to distinguish insulating materials operating at different temperature levels. Letters were used for different designations. Letter classifications have been replaced by insulation system temperatures in degrees Celsius. The system temperature is the maximum temperature at the hottest spot in the winding (coil). These systems are used by Acme Transformer for a large part of the product line.