4th step SSQ Flashcards
- What is the equation for determining a transformer’s turns ratio?
Np- Number of turns on the primary
Ns- Number of turns on the secondary
Vp- Voltage on primary
Vs- Voltage on secondary
Reference: 2nd step transformer theory and design
- Determine the turns ratios for the following single-phase transformers.
a. 16 kV to 120 V
b. 16 kV to 240 V
C 12 kV to 120V
d. 12 kV to 240V
A.133:1
b.66:1
C.100:1
d.50:1
Reference: 2nd step transformer theory and design
What are the two polarities a transformer can have?
Additive and subtractive.
Single-phase transformer nameplates indicate whether its polarity is additive or subtractive. Polarity indicates the relative direction of current flow through the transformer. Polarity is determined by looking at the “polarity bushing” (H1) on the transformer, and its relation to the X1 bushing. When H1 and X1 are on the same side, it is considered subtractive polarity. When H1 and X1 are on opposite sides, it is considered additive polarity. With standard markings, if the direction of current flow is from H1 to H2, the current flow will be in the direction of X2 to X1.
Reference: 2nd step transformer polarity
What is the purpose of a transformer tap changer?
To raise or lower secondary voltage by changing the turns ratio
Taps on transformers allow the turns ratio to be changed over a small range. This gives some flexibility for adjusting the operating voltage of the transformer. Each tap changes the turns ratio by some small amount, typically 2.5%. The taps consist of terminals, linkages or similar devices.There are two types of tap changers: no load tap changer and load tap changer. No load tap changers require the transformer to be de-energized, so there is a short interruption in customer service while the taps are changed. Load tap changers provide the ability to change taps while the transformer is energized and without interrupting the flow of current through the transformer and to the customer.
Reference: 2nd step Transformer Design and Theory
How is rotation checked/determined?
At the customers panel using a phase sequence indicator, from L to R (RWB) attach clips to customer’s phases.
Reference: 4th Step Vectoring Training Manual
What is the maximum weight allowable for a closed-delta 300 kVA transformer bank on a 50-foot wood pole using a transformer mounting bracket? What is the minimum diameter pole for this application?
4,250 Ibs.
H2 class
11 inch minimum diameter.
Reference: DAP Table AP 106-1, and AP 132-1 Note 7
What is the maximum weight allowable for a 2-single phase transformer bank (open delta) hung on a wood pole using a transformer bracket?
1,600 Ib total weight limit.
Reference: DOH, Figure AP 122-1
Describe the AC electrical characteristic of impedance.
Impedance opposes the flow of electrical current in an AC circuit. It is made up of two components: resistance and reactance. Since reactance is at a 90-degree angle to resistance, resistance and reactance are added with vectors in order to calculate impedance.
Reference: 4th Step Ohm’s Law and Power Formulas Training Manual
When - and why - is the wye leg tied, on the primary side of a 4 kV bank?
Open Wye banks (2 transformers) shall be connected to the system neutral.
Closed Wye- delta banks (3 transformers) - Wye-Delta you float
shall not be connected to the system neutral. When wiring a delta secondary, the delta is left open to check that voltage is less than 20 volts. Recall that a disadvantage of wye-wye connected transformers is that they do not trap third harmonics. Therefore, the wye must be connected to the neutral until the delta voltage is checked and then the delta is closed to provide a path to circulate the 3rd harmonic currents. After the delta is closed, the wye connection is floated
Tied for checking voltage.
Wye- Wye banks (3 transformers) Wye-Wye you tie
A disadvantage of wye-wye connected transformers is that they do not trap third harmonics. This will be discussed in more detail in the Voltage Problems training module. Because all harmonic voltages are in-phase, it results in phase currents that do not cancel in a wye. Therefore, there is no path for the 3rd harmonic currents when the wye is floated When the wye point is connected to the system neutral, it provides a path for the in-phase 3rd harmonic currents. Because these currents are additive, they add and can cause high unnecessary neutral currents
It is tied to get rid of the third harmonics
Reference: 2nd step transformer delta vs wye
What is a high leg? How is it identified?
A high leg is the secondary phase with the highest phase to ground voltage.As required by the National Electric Code, the high phase (power leg) must be prominently identified by orange markings on the cable or bus.
Reference: DOH, T 454 Note 4
In a three-phase circuit, what is a grounded leg? Where is it located in the customer’s panel?
A grounded leg is a phase that has been grounded. It is generally located in the middle position in the customer’s panel.
When and why is rotation checked?
The need for a phase sequence meter is to identify the rotation of a three phase source and to ensure that the equipment can be reconnected to the source with the proper rotation. Before taking a piece of equipment out of service, the rotation should be checked and recorded. Then, after the work has been completed, the rotation should be rechecked before the equipment is re-energized.
Reference: 4’ Step Vectoring Training Manual
How is improper rotation corrected
Without disturbing the high-leg, swap any two phases.
Reference: 4’ Step Vectoring Training Manual
If two 10 kVA transformers are wired in an open-delta configuration - for 3-phase power - what would be the available kVA?
20 kVA x0.86 = 17.2 available kVA.
Reference: 4’ Step Wiring Three-Phase Banks Training Manual
What are the thumb rules for determining amps per kVA for the following secondary voltages?
a. 120 V single-phase
b. 240 V single-phase
480 V single-phase
d. 240 V three-phase
e.480 V three-phase
f.208 V three-phase
a. x8
b. x4
c. x2
d. x2.4
e. x1.2
f. x 2.8
Reference: pocket manual
What is TS-5, and when is it used?
2.1 Applicability
This procedure shall be used to field-test all newly installed and relocated overhead transformers, and all overhead transformers with blown fuses.
1.0 purpose
This procedure outlines the requirements for in-place field-testing of overhead transformers. It is to be used for:
* Newly installed or relocated transformers
* Re-energizing existing transformers with blown fuses
* CP transformers with tripped overload breakers
Reference: DOM, TS-5 1.0
When applying TS-5 to newly installed/relocated transformers, how are the transformer secondaries grounded (prior to energization).
For grounded secondaries, connect the secondary ground. For ungrounded secondaries, temporarily install a solid ground on the low side at any of the phase connections or the neutral. (The intent is to ensure enough fault-current to blow the test fuse for a primary to secondary fault.)
Reference: DOM, TS-5 4.1
Distribution Apprentice Lineman OJT
When are clearances required?
Clearances are required to work on de-energized generating station or substation apparatus or equipment which is normally energized above 600 volts.
Clearances are required to work on de-energized lines or line sections above 600 volts.
Reference: APM Rule 105
When are no-test orders required?
No Test Orders (definition DOM)
For hazardous line construction work, Edison makes available “No Test Orders” (NTO) to every foreman. Once NTO’s are issued, if the line relays, it will not be tested until contact is made with the foreman they were issued to and he cancels his NTO
DOM SOB 314
A No Test Order is a formal statement issued and recorded under a prescribed procedure, by an authorized person to a qualified person, declaring that in case certain specified energized distribution line(s) or substation equipment of 33 kV or below become de-energized, said equipment shall not be re-energized, by any method, until the No Test Order has been released by the person to whom the No Test Order was issued.
The purpose of the No Test Order is to provide a formal procedure by which a qualified person could request and receive a guarantee that a line or equipment shall not be re-energized when the nature of the work is such that the re-energizing would be hazardous to personnel.
APM 233-No Test Orders shall be taken during Distribution arc flash hazardous work activities that could cause an Arc Flash when either working at MAD or within the Arc Flash Boundary (AFB). When performing Rubber Gloving or Hot Sticking
Reference: SOB 314 and APM Rule 233
Why is it important that the correct size fuse be used in distribution circuits? What could result from installing a fuse that is either too weak or too heavy?
Fuses which are too weak may blow out during normal operating current loads. Fuses which are too heavy may fail to protect associated transformers (or other equipment).
Reference: 4thStep Fuses Theory and Operation Training Manual
What are current transformers (CTs) and potential transformers (PTs)? What are their typical applications in distribution circuits?
CTs are transformers which reduce high currents to safe levels for relay protection and metering services.
PTs are transformers which reduce high voltage levels to safe levels for equipment operation and metering services.
Reference: 4th Step Metering Theory and Operation Training Manual
How is a PT typically connected in a 2400 V application, and what is the typical turns ratio for this PT?
2400 V PTs are normally phase-to-ground connected.
The typical turns ratio is 20:1.
Reference: 4th Step Metering Theory and Operation Training Manual
What is the load on the following transformer (120/240 V, 10), given the following data:
VA = IxE
VA = (20 A +30 A) x 120 V = 6000 VA or 6 kVA.
Reference: 4th Step V, I, and P Relationships Training Manual
What is the load on the following transformer bank (120/240 V, 30), given the following data:
VA=I x E x 1.73
VA= 117A x 240V x 1.73
VA= 48,636
kVA=48.6
Reference: 4’ Step V, I, and P Relationships Training Manual
What is the equation for determining the load on a transformer bank with unbalanced loads?
VA=[(IA+IB+IC)/3] x E x 1.73
Reference: 4th Step V, I, and P Relationships Training Manual
Are pole-mounted grounds allowed in the climbing space? If so, what provisions must be observed?
2.4-one vertical run of PGW is allowed in the climbing space without the use of wood molding
3.3-Only one wood-covered ground wire is permitted in the climbing space.
Reference: DOH, GR 100.2.4 and 100.3.3
Are pole-mounted grounds allowed in the climbing space of rack construction?
No. Only one wood-covered ground wire is permitted in the climbing space. In rack construction, grounds are not permitted in the climbing space per G.O. 95, Rule 54.9-F.
Reference: DOH, GR 100.3.3
- What is the safe working load limit of a 1-1/8” 2-in-1 double braid polyester core and cover winch line?
7.000 Ibs
Reference: Rigging Standards Manual, Table 11
- What is the working load limit of a handline sheave?
1,000 Ibs
Reference: Rigging Manual, Figure RM 4-8
When using a hand hoist, is it acceptable to use the chain and hook in a choker configuration? Why or why not?
No. The hook will break under stress.
Reference: Rigging Standards Manual, Figure 147
- What are the three basic nylon sling hitches?
Straight Pull
Choker Hitch
Basket Hitch
Reference: Rigging Manual, Figure RM 7-2
If a lineman has any doubt regarding the type or size of rigging equipment for a lift what should they do?
Contact their supervisor.
Reference: Rigging Manual, Making Lifts 8.2.
For what circumstance are pole grounds butt-wrapped on the pole? How is this accomplished?
Use in rocky soil where it would be impossible to drive ground rods.
Use PGW wire with 10’ of protective covering removed (or bare wire) on bottom of pole, and staple in place.
Reference: DOH, Figure GR 105-1
What is the maximum tank temperature for a transformer?
By design, the maximum internal temperature rise in a transformer at full load can be 115 °F (65 °C); this can increase to a 155 °F (88 °C) rise at 160 percent of rated load. Under no circumstances should the maximum tank temperature (ambient plus tank temperature rise) exceed 265 °F (130 °C).
Reference: DOM, TE-5 4.1 Table 5-1
What activities are prohibited when working from a boatswain chair suspended from a fiber rope?
Welding, burning, or sandblasting
Reference: APM Rule 130.h
When making a lift with tackle blocks, how is friction accounted for?
The rigging industry recognizes a 10% friction factor for each sheave in any given rigging scenario.
Reference: Rigging Manual, 5.1.3.A
37. What does the term “wind loading” mean? What are the wind standard wind load values used by SCE?
Wind loading refers to the pressure - in pounds per foot (lb/ft) - exerted on poles. The standard wind loading value is 8 lb/ft, while 6 Ib/ft, 12 lb/ft, and 18 Ib/ft are also used.
Reference: DDS-10. 5.2
What does the term “wind loading” mean? What are the wind standard wind load values used by SCE?
Wind loading refers to the pressure - in pounds per foot (lb/ft) - exerted on poles. The standard wind loading value is 8 lb/ft, while 6 Ib/ft, 12 lb/ft, and 18 Ib/ft are also used.
Reference: DDS-10. 5.2
How often is MSA Altair gas analyzer calibrated? How often are functional tests performed?
The gas monitor shall be calibrated within 30 days prior to being used.
The accuracy of the instrument must be functionally checked with a known concentration of gas before each day’s use. This is referred to as a “bump test.” This is accomplished by applying calibration gas to the monitor until all sensors alarm
Reference: DOM, TE-13 2.2, 2.3
. If bayonet fuses must be used to de-energize a fused PM transformer, what is the maximum amperage that can be dropped? How is the load determined?
If a transformer is to be de-energized using the BON fuses, verify that the amperes through each BON fuse is not in excess of 100 A. Measure the primary current to the transformer. Measure the primary current feeding through the transformer to other load (if applicable). Subtract the feed through current from the current to the transformer. If this is less than 100 A, then the BON fuses may be used to de-energize the loads.
Reference: DOM, TR-2 Attachment 2-5 step 2
May PMHs or PMEs be used to de-energize capacitor banks? Explain?
PMH and PME switches cannot be used for capacitor switching. A sign reading “Capacitor Bank No. Source-Open Capacitor Bank Switch Before Opening This Switch” shall be placed on the compartment door of all PMH/PME switches used to feed capacitor banks.
Reference: DOM, SW-6 2.1
. Concerning riser construction: no step or kick block shall be installed below what height on a pole?
- See DOH PO 100.4 for pole step requirements. No step or kicker block should be placed below the 9 foot level.
Reference: DUG, Figure CR 110-1 Note 4
When should the automatic circuit recloser be made non-automatic in underground distribution circuits?
- Automatic Circuit Recloser Operation
a. No test orders will be taken on all circuits in an underground structure whenever the following work activities will be performed: - Testing, grounding, cutting, spiking, repairing cable or components normally energized above
600 V. - Disassembling cable components normally energized above 600 V.
- Installing or removing electrical or communication cable.
- Relocating energized high-voltage underground cable or equipment.
- Filtering or replacing oil on energized high voltage underground equipment.
- Operating energized loadbreak components.
- Immediately following a high-voltage failure.
Reference: APM Rule 316
. What steps are taken prior performing work on padmount capacitors?
The following procedures shall be completed prior to performing work on capacitors of any voltage:
1. The capacitors shall be de-energized using the capacitor switches provided.
2. Visually check the capacitor switches open. If any are closed, open manually with live line tools.
3. Check for elimination of current flow with clamp-on ammeter.
4. The source switch position to the capacitor switches shall be opened, locked, and tagged. Using live line tools, the primary terminals to the capacitor installation shall be tested de-energized and grounded.
5. After waiting a minimum of five minutes from de-energizing, the capacitor terminals shall be shorted by means of temporary jumpers and adequately bonded to the case and grounded, using live line tools.
Reference: APM Rule 317.b
Which type of fuses are used in a load-break fuse cabinet (LBFC)?
Current-limiting fuses (CLFs).
Reference: DUG, PD 442.1.2
Explain APM Rule 307, “Moving Underground Cable.”
a. All in-service cables that are to be moved shall be carefully inspected before and after moving.
b. Cables energized in excess of 600 volts shall be moved only under the direction of the supervisor or employee in charge.
Reference: APM Rule 307
Upon entering an underground structure, an employee observes evidence of structural compromise, and flexing concrete. According to the DOM, what actions shall the employee take?
5.2 Required response to conditions listed in subsection 5.1
A. Employees will inform their immediate supervisor.
B. Employees will mitigate the hazard to the extent possible, which may include installing remote switching or other isolation methods.
C. The supervisor in charge will notify the Switching Center of the condition and that a temporary “CAUTION DO NOT ENTER WHILE EQUIPMENT IS ENERGIZED” sign was posted, and will prepare a circuit map revision noting the structure is “Closed When Energized.”
Reference: DOM, IM-5 5.2
. According to the APM, when may underground cable be considered de-energized?
- According to the APM, when may underground cable be considered de-energized?
Cable and equipment shall be considered energized and worked with adequate protective devices until it has been tested de-energized with an approved device for indication of voltage and grounded with approved ground devices.
Reference: APM Rule 306.b
As it applies to a current transformer (CT) used in metering, how is a CT’s overload capability determined?
Overload capability is the ampere rating multiplied by the rating factor.
Briefly explain PM Rule 147, Working Distance. What are the approach distances for 4 kV, 12 kV, and 16 kV circuits? May those distances be reduced?
No employee shall approach or take any conductive object, except with approved devices, closer to unprotected energized parts than shown in the following table:
Approach distances may be reduced, provided adequate approved protective devices are used. Such protection shall be applied and removed with approved insulating devices.
Contact shall not be made with protective devices on conductors energized above 7,500 volts except with live line tools.
EXCEPTION: Employees certified in rubber gloving of conductors energized between 7,500 volts to 17 kV may contact protective devices up to 17 kV while wearing rubber gloves rated for the voltage and while utilizing “insulate and isolate” work practices.
Reference: APM Rule 147
