Term
| List 7 ways Xcel generates Electricity |
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Definition
Coal
Natural Gas
Petroleum
Nuclear
Hydro
Wind
Solar |
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Term
| What Generation Voltages does Xcel use? |
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Definition
13.8KV
15.5KV
18KV
20KV
22KV
24KV
27KV
(generation voltages vary from 11KV to 33KV) |
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Term
| What 3 things are required to induce voltage? |
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Definition
-
- Magnetic Field
- Conductor
- Relative motion between the 2
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Term
| List 5 Transmission Voltages |
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Definition
44KV
69KV
115KV
230KV
345KV |
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Term
| List Primary Feeder/Distribution Voltages |
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Definition
2400/4160 = 4KV system
7200/12470 = 12.4KV system
7620/13200 = 13.2KV system
14400/24940 = 25KV system |
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Term
| List Xcel's Distribution Secondary voltages. |
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Definition
120/240 = 1 or 3 phase
120/208 = 1(network) or 3 phase
240/480 = 3 phase
277/480 3 phase
240 & 480 ar power banks (3W3phase) |
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Term
| Define Isolation Transformer |
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Definition
An electrical device, which through the mutual induction in coils of wire, changes a given voltage to a desired voltage whil maintaining frequency. (up or down)
2 separate coil windings -high/low-
1 core |
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Term
| 3 types of transformer loss |
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Definition
eddy current
copper
hysteresis (collapse/expansion of mag field) |
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Term
| 2 types of transformer cores |
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Definition
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Term
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Definition
High voltage side of transformer
smaller wire, more turns
2400v x 50amps = 120kva in
Low voltage side of transformer
bigger wire, less turns
240v X 500amps = 120kva out
(max amps xfmr can handle continuously) |
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Term
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Definition
The number of turns of wire on the HV side compared to LV side.
Directly proportional for voltage
(10:1)
Inversely proportional for amperage
(1:10) |
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Term
| What is the most common reason for Transformer Failure? |
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Definition
Overload, which causes overheating.
AWG (winding wire size) determines how much current can flow without overheating |
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Term
| List 3 Transformer cooling methods |
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Definition
Ambient Air
Forced Air
Oil (mineral, etc) |
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Term
| What is used to troubleshoot Transformer problems and measure resistance? |
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Definition
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Term
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Definition
- Auto
- Dry
- CSP
- Conventional
- Current
- Potential
- Power
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Term
What is CSP?
List 4 secondary breaker positions.
List 4 features. |
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Definition
Completely Self Protected
Closed, Open, Light, Reset
- HV lightning arrestor
- Internal HV fuse
- LV secondary breaker
- Overload Switch (boosts ampacity for a short time)
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Term
| Explain Conventional Transformer |
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Definition
1 or 3 phase
x/s fuse and lightning arrestors
1 or 2 HV bushings
2,3 or 4 LV bushings
Internal or external tap changers
Mostly used on feeders |
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Term
| Explain Power Transformer |
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Definition
- Large transformers (500KVA and above)
- Used in substations (transmission & Distrb)
- Contain lightning arrestors, load rated tap changers and oil level indicators.
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Term
| Explain Auto Transformers |
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Definition
Uses only 1 winding for both primary and secondary. (physically connected unlike isolation xfmrs)
Used to increase/decrease line voltages and to regulate large powerlines.
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Term
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Definition
Uses CTs & Pts (1 or 3 phase)
Large customers (4000 amps and above)
Cost saving for Xcel and customer
Interval data downloaded monthly |
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Term
| Explain Dry Pack Transformer |
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Definition
Generally smaller xfrms used commercially to step up or down voltages.
No oil. Ambient air cooled.
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Term
| Explain Pad Mount UG transformer |
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Definition
1 or 3 phase enclosed xfrmer with all connections inside.
1 to 3 bayonette fuses (HV)
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Term
| Explain the difference between Series and Parallel secondary windings in regards to amps/volts. |
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Definition
Series gives 2 voltages, but 1/2 the ampacity.
Parallel gives 1 voltage, but double the ampacity.
(also doubles turns ratio) |
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Term
What determines how many secondary bushings on the following?
2 bushing
3 bushing
4 bushing |
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Definition
2 bushing = single secondary nameplate rating
(120, 277, 277/480)
4 bushing = greater than 100KVA
3 bushing = everything else
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Term
| Explain transformer polarity |
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Definition
Additive = 8660v or less & 200KVA or less
Subtractive = (anything else)
8661v or more
or
201KVA or more
polarity determines bushing layout
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Term
| What does GRDY indicate on the nameplate? |
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Definition
| A reduced BIL (basic insulation level) on the H2 bushing. |
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Term
| What does 240/120 indicate on a nameplate? |
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Definition
| UG transformer with a single secondary winding with a permanent center tap. |
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Term
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Definition
- Opposition to current flow
- Expressed in Ohms
- Not measured, but calculated
- Based on % of voltage drop from no load to full load
- Includes Resistance, Inductance & Capacitance
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Term
Explain the difference between:
System Voltage Tap Changers
&
Regulation Tap Changers |
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Definition
System- allows voltage to be adjusted to suit the primary voltage requirements. Not load rated.
Used for cutovers, Inventory reduction, multiple system voltage uses
Regulation- Regulates Secondary output voltage by lenghtening/shortening the windings. Load rated. Used to keep secondary w/in +/-5% as per PUC. |
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Term
| What are the 5 voltages on a multi-position Tap Changer? |
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Definition
- 14400
- 13800
- 13200
- 12870
- 12540
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Term
| What must be considered when paralleling transformers? |
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Definition
Must have identical Voltage ratings, tap settings, and frequencies.
Impedance must be w/in 15% (+/- 7.5%)
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Term
| List some advantages to 3 phase power over 1 phase. |
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Definition
3 phase motors smaller for same horse-power
More even output/120 degrees apart
(never falls to zero)
Smaller conductors / more efficient
Neutral carries current for imbalanced load.
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Term
| What is the max amp formula for secondary 3 phase? |
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Definition
Total KVA x 1000
1.732 x secondary voltage (0 to 0)
= max amps per leg |
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Term
| What must be considered when "banking" transformers? |
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Definition
Identical Voltage ratings, Tap settings and frequencies
Impedance w/in 15%
Similar KVA ratings
Polarity
Bil Rating |
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Term
Explain:
Inductance
Capacitance
Resistive |
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Definition
L=Inductive loads: motors/xfmr windings
ELI = Voltage leads current
C=Capacitive: cap banks counteract inductive loads
ICE = current leads voltage
(purely) Resistive curcuit = unity power |
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