S3 - Distribution Transformers Flashcards
The winding of the transformer which is connected to the source of power.
Primary Winding
The winding of the transformer which delivers power to the load
Secondary Winding
The magnetic circuit upon which the windings are wound
Core
One which is rated for the higher voltage
High-tension Winding
One which is rated for the lower voltage
Low-tension Winding
A constant-voltage transformer so connected that the delivered voltage is greater than the supplied voltage
Step-Up Transformer
A constant-voltage transformer so connected that the delivered voltage is less than that supplied
Step-Down Transformer
Consists of separate insulated electric windings for the different phases, wound upon a single core structure, certain portions of which are common to the different phases
Polyphase Transformer
Consists of several one-phase transformers with separate electric circuits but having certain magnetic circuits in common
Polyphase Transformer
The ratio of primary to the secondary voltage, depends primarily upon the ratio of the primary to the secondary turns
Voltage Ratio
The inverse ratio of the turns in the two windings
Current Ratio
The change in secondary voltage from no load to full load
Regulation of a Transformer
The ratio of the output to input or, in other words, the ratio of the output to the output plus the losses
Transformer Efficiency
Determined by the resistances of the high-tension and low-tension windings and of the leads
Copper Losses
Used by electric utility companies to step-down the distribution primary voltage to a secondary service voltage to be used by the customer
Distribution Transformer
This is equal to the sum of the losses in the iron core. These losses consist of eddy-current losses and hysteresis losses
Iron Losses
Can a “Quick Check Tester” be used on an energized transformer?
No - the unit should never be used on an energized transformer
Can the CSP secondary breaker be used as a clearance point?
No - there is not a visible open point
What is the maximum current rating of a single 4/0 Aluminum quadraplex service?
258 Amps
What is the recommended pot-lead size for a 3-pot, 277/480 V transformer bank with three 167 kVA transformers?
500 KCM Copper
What is the power in kW if you have a heater pulling 420 Amps on a 1-phase 240 volt circuit?
P = EI = 420 * 240 = 100,800 Watts = 100.8 kW
What should the fuse size be for a 3-pot, 4kV where all 3 transformers are 100 kVA units?
65T
What is the EPB standard primary connection for 120/208 V, 3-pot bank?
Wye Connected ( TC-10)
A Troubleman is asking whether the primary common connection of a 4W, 3P, 120/240 V, 3-pot wye-delta transformer bank should be grounded, what is your answer?
No – the Wye common connection should be floated (TC-2, note 1; TC-6, note 1)
What is the maximum summer loading in secondary amps of a 240 Volt, 3 Wire, 100 kVA Transformer?
521 Amps
On a 3P, 4W 120/240 V, open delta transformer bank the common primary connection is floating, is this OK?
No, the transformer tank ground MUST be connected to the system neutral (TC-4, note 3)
A single-tank, 3P, 4W, 120/208 V, 300 kVA transformer has (1) 500 MCM Copper transformer lead per phase, is this correct?
No, the transformer should have (2) 500 MCM Cu leads per phase (Drwg No: A-4599, sheet 2 of 2)
