Single-Phase Underground Operating - SaskPower 3 Book 2/4. SINGLE-PHASE... · When operating in an underground single-phase system, an understanding of the causes of faults, and fault

March 31, 2005

S T U D E N T M A N U A L

Single-Phase Underground

Operating

Copyright 2004 by the Training and Development Centre, SaskPower. All Rights Reserved

2 S T U D E N T T R A I N I N G M A N U A L

Prerequisites: • Introduction to Underground Systems module

Objectives: Given an underground distribution system, the Constructions Standards manual, tools and equipment, and an electrical facilities map, you will be able to perform the necessary switching procedures to operate an underground system.

Rationale: There are a variety of procedures required for the operating, troubleshooting and maintenance of an underground distribution system. All of these procedures require the ability to perform a combination of basic operating techniques. Since many components of an underground system are not visible, it is important to develop and follow standard switching procedures.

Learning Objectives• Identify fault situations in an underground distribution system.• Explain the procedure to fuse and operate a live front transformer.• Demonstrate the procedure to fuse and operate a live-front

transformer.• Demonstrate the procedure to fuse and operate a dead front

transformer.• Review the purpose and layout of a switching plan for underground

switching.• Demonstrate the procedure to perform switching in an underground

system.

Learning Methods• Self-learning + On-the-job• Self-learning + On-the-job• On-the-Job Demonstration and Practice• On-the-Job Demonstration and Practice• Self-learning + On-the-job• On-the-Job Demonstration and Practice

EVALUATION METHODS

• Written test

S I N G L E - P H A S E U N D E R G R O U N D O P E R A T I N G 3


• Written test• On-the-Job Evaluation• On-the-Job Evaluation• Written test• On-the-Job Evaluation

STUDENT RESOURCES

• Underground Tools module

Learning Steps1. Read the Learning Guide.2. Follow the steps outlined in the Learning Guide.3. Clarify any questions or concerns you may have.4. Complete the Practice and Feedback.5. Complete the Evaluation.



Lesson 1: Underground FaultsLearning Objective:Identify fault situations in an underground distribution system.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Introduction

Operating is performed mainly at transformers where switching andfusing capabilities are readily accessible. Underground switching isoften required due to underground faults. Some historical causes offaults include:

• Lightning can damage underground systems.• Faulty splices and cable terminations due to moisture or thermal

(heat) failure.• Contamination of cable terminations (dirt or salt) leads to tracking

and eventually the breakdown in cable insulation.• Cable flaws incurred at the manufacturer, or improper handling of

the cable (i.e. the bending radius exceeded prior to burying).• Mechanical damage from improper backfill or back-filling

techniques; stones, cement or other objects accidentally placed on top of the cable could puncture it.

• Immediate failure can occur during excavation.• Cable failure can occur in older cables from animals such as moles.

Newer cables are chemically equipped to prevent animal damage.

When operating in an underground single-phase system, anunderstanding of the causes of faults, and fault locating are requiredskills.

The knowledge of these basic operations can assist the operator inlocating and repairing faults on the underground system.

Most underground system faults occur in the ground and cannot be seen.Specialized equipment and techniques must be utilized to separate thefault from the rest of the system. To do this, first determine whichsection of cable the fault has occurred at.

The faulted cable is then isolated by using approved switching methodsto temporarily restore power. Try to pinpoint the cable fault using faultlocating devices. Specially trained personnel and equipment may be



required to find the fault.

Finding Underground Faults (loop system)

When a fault occurs on an underground system, the nature of the faultmust be determined.

If the take-off fuse has blown, check the transformer fault indicators todetermine what section of the line has faulted.

If the take-off fuse has not blown, perform a voltage check at thetransformer in question to determine if the transformer fuse has blown.If the voltage on the secondary bushings is in accordance with thetransformer nameplate ratings, the operator can suspect the secondarycable as the problem.

If there is no voltage on the secondary bushings, remove the secondarycables from the transformer bushings and re-fuse the transformer. If thetransformer fuse blows again with the secondary cables removed, thetransformer must be replaced.

If the transformer fuse holds with the secondary cables removed, thetransformer is operational and the problem lies in the service cable.



Lesson 2: Fusing Underground Live Front TransformersLearning Objective:Explain the procedure to fuse and operate a live front

transformer.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Introduction

When operating a single-phase underground distribution system,operators are required to fuse in two main types of devices.

• live front• dead front

The procedure to fuse these transformers requires specific techniques.

Live Front

The fuse in a live front transformer is located in the centre of thetransformer buss assembly, and is identified by being slightly larger thanthe outer two arc stranglers.

Reference

For further information on live front transformers, refer to theUnderground Tools module and Underground Apparatusmodule.

---Note---When removing the fuse or arc strangler, it must be left in avisual location.



Dead Front

The following steps are guidelines to follow when operating in a deadfront transformer:

• Open and secure the transformer door.• Operate the transformer relief valve. This will relieve the internal

transformer tank pressure and prevent oil from spilling when thefuse is removed.

• Consult the Construction Standards manual for proper fuse size.• When replacing the fuse cartridge, ensure the serrated end is

tightened last.

---Note---When placing the arc strangler in the saddle, be sure to cock themechanism.

CAUTION!Never leave an open arc strangler or fuse in its saddleas it is energized and may short out in the door.Remove it and store in an accessible location.

DANGERSTOP

The buss assembly is still energized when the fuse isremoved. Always maintain the recommended limits ofapproach when working around the buss assembly.

---Note---Upon replacing the bayonet fuse, ensure the collar is locked intoplace.

---Note---Do not use the bayonet fuse to pick up the transformer load.



CAUTION!The bayonet fuse is not designed for fault closing.Serious personal injury may result from internaltransformer fault conditions, causing a rupture or thecover to blow off. Always energize the transformerfrom a remote location.



Lesson 3: Procedure to Fuse and Operate a Live-Front TransformerLearning Objective:Demonstrate the procedure to fuse and operate a live-front

transformer.Learning Method:On-the-Job Demonstration and PracticeEvaluation Method:On-the-Job Evaluation



Skills Practice

1. Tools:

1. Clean and approved 8 foot grip-all hotstick.

2. Removal of fuse:

1. Open and block the transformer door.

2. Attach the hotstick to the fuse eye and pull open.

3. Retract the hotstick handle fully and remove the fuse.

3. Installing a fuse:


2. Cock the fuse.

3. Install the fuse (with hotstick) in the saddle.

4. Ensure the fuse is still cocked and with a positive motion,close the fuse into position.



Lesson 4: Procedure to Fuse and Operate a Dead Front TransformerLearning Objective:Demonstrate the procedure to fuse and operate a dead front

transformer.Learning Method:On-the-Job Demonstration and PracticeEvaluation Method:On-the-Job Evaluation



Skills Practice

1. Tools:

1. Clean and approved 8 foot grip-all hotstick

2. Crescent or box end wrenches

2. Removal of fuse:

1. Open the transformer door.

2. Open the relief valve, using an 8 foot grip-all hotstick.

3. Unlock the bayonet fuse latch, using an 8 foot grip-allhotstick.

4. Push the bayonet fuse down and rotate the handle 90degrees.

5. Pull the bayonet fuse out 75mm and wait a few seconds.

6. Completely remove the bayonet fuse.

7. Using a wrench, remove the fuse from the fuse cartridgecontainer.

3. Installation

1. Install the fuse into the fuse cartridge container andconnect to the bayonet assembly using a wrench.

2. Insert the bayonet fuse assembly into the transformer fusetube housing.

3. Turn the locking handle until the latch engages the tubehousing.

4. Close and secure the transformer door.



5. Use appropriate switching methods to energize thetransformer from a remote location.



Lesson 5: Switching PlanLearning Objective:Review the purpose and layout of a switching plan for

underground switching.Learning Method:Self-learning + On-the-jobEvaluation Method:Written test

Introduction

The purpose of a switching plan is twofold:

• safety• efficiency

The design of the switching plan is to isolate cables or apparatus whilemaintaining electrical service to as many customers as possible. Thefollowing must be considered:

• radial system, loop system or a combination of both• normal open locations• location and size of reactors• location of the apparatus to be switched out• safe order in which the switching can be done

A switching plan must include the following:

• date of when the switching is to take place• land location(s) of where the various switching procedures are going

to be completed• out and in procedures to be completed at each location -these should

be in order and in conjunction with the other locations

As you can see from the switching plan example on the following page,the procedure number, land location, type of operation, time, worker,and general remarks are all included. All of the operations for out and



in procedures can be documented.

Figure 1. Switching Plan

CAUTION!Each worker must get a copy of this plan and follow itaccordingly. The individual in charge willcommunicate all operations to the workers.



Figure 2. Underground Single-Phase Loop Feed

Underground Loop System

On occasion, due to construction or maintenance, it is necessary to eitherisolate a cable, transformer or change a transformer bushing. Theseprocedures usually involve moving a normal open in order to maintainelectrical service.



In order to successfully complete the task and provide safe and reliableservice, two steps are required:

• closing the normal open• isolating underground apparatus

Closing the Normal Open

When underground maintenance or construction situations in a loopfeed warrant a switching procedure, it will usually involve closing thenormal open in order to maintain electrical service.

---Note---The normal open is incorporated in an underground system toavoid large outages.

DANGERSTOP

When operating underground equipment, alwaysmaintain the required clearances from energizedparts.



Lesson 6: Perform Switching in an Underground SystemLearning Objective:Demonstrate the procedure to perform switching in an

underground system.Learning Method:On-the-Job Demonstration and PracticeEvaluation Method:On-the-Job Evaluation



Skills Practice

1. Procedure to close the normal open in a dead front, load break, underground transformer.

1. Clean an approved 8 foot grip-all hotstick and elbow pullerhotstick.


3. Remove the arrestor or insulated cap in the H1B bushingwith an elbow puller hotstick.

4. Remove the arrestor or insulated cap from the feedthroughwith an elbow puller hotstick.

5. Remove the cable elbow from the feedthrough and installon the transformer H1B bushing.

6. Remove the arrestor or insulated cap ground leads with an8 foot grip-all hotstick.

7. Remove the feedthrough with an 8 foot grip-all hotstick.

8. Remove the feedthrough ground lead.


2. Procedure to close the normal open in a live front load break transformer.

1. Clean an approved 8 foot grip-all hotstick


3. Cock the arc strangler.

4. Install the arc strangler into the vacant saddle using an 8foot grip-all hotstick.

5. Close the arc strangler into position.




3. Procedure to isolate a faulted cable in an underground loop feed system (dead front, load break), Location A:

1. Clean an approved elbow puller hotstick.

2. Clean an approved 8 foot grip-all hotstick.

3. Inspect the underground grounding or operating kit.

4. Install the feedthrough and attach its ground lead using an8 foot grip-all hotstick.

5. Remove the faulted cable and install on the feedthroughusing an elbow puller hotstick.

6. Install ground leads for the arrestors or insulated capsusing an 8 foot grip-all hotstick.

7. Install arrestors or insulated caps on the feedthrough andtransformer bushing using an elbow puller hotstick.

8. Close and secure the transformer door

4. Procedure to isolate a faulted cable in an underground loop feed system (dead front, load break), Location B:

1. Install the feedthrough and attach its ground lead using an8 foot grip-all hotstick.

2. Remove the faulted cable and install on the feedthroughusing an elbow puller hotstick.

3. Install the ground leads for the arrestors or insulated capsusing an 8 foot grip-all hotstick.

4. Install the arrestors or insulated caps on the feedthroughand transformer bushing using an elbow puller hotstick.




5. Procedure to isolate a padmount transformer (dead front, load break).

1. Clean an approved 8 foot grip-all hotstick.

2. Clean an approved elbow puller hotstick.

3. Inspect the underground grounding or operating kit.


5. Install the feedthrough ground lead using an 8 foot grip-allhotstick.

6. Install the feedthrough on the transformer parking standusing an 8 foot grip-all hotstick.

7. Remove the cable elbow from the H1B bushing and installon the feedthrough using an elbow puller hotstick.

8. Remove the cable elbow from the H1A bushing and installon the feedthrough using an elbow puller hotstick.


6. Procedure to change a bushing or insert a Y bushing on a padmount transformer (dead front, load break).

1. Isolate and ground the cables at the transformer using theappropriate method.

2. Remove the bushing by turning it counter-clockwise.

3. Install the new bushing or Y insert by turning it clockwise.

4. Connect the bushing ground strap to the transformer.

5. Apply a light coating of approved silicon grease to thebushing.



6. Install the cables on the feedthrough and drop them into thebottom of the transformer well.



Summary

To summarize this module, you have learned:

• The procedure to fuse and operate a live front transformer.• The procedure to fuse and operate a dead front transformer.• The procedure used to prepare a switching plan.

Practice Feedback

Review the lesson, ask any questions and complete the self test.

Evaluation

When you are ready, complete the final test. You are expected toachieve 100%.



Review Questions

1. Some causes of underground faults are:(a) Faulty splices and cable terminations.(b) Cable flaws and contamination.(c) Mechanical damage.(d) All of these

T / F 2. The operator should check the take-off fuse first when troubleshooting underground faults.

T / F 3. When troubleshooting underground faults, the operator should check the take-off fuse first.

T / F 4. The knowledge of basic operating in a single-phase underground system can assist the operator in locating and repairing faults.

T / F 5. Fault indicators don’t assist the operator in finding faults.

6. When operating in a single-phase underground distribution system, operators are required to fuse:(a) Two types of transformers.(b) Three types of transformers.(c) Four types of transformers.(d) One type of transformer.

T / F 7. When re-fusing a live front single-phase transformer, an operator must use an elbow puller hotstick.

T / F 8. Always leave the arc strangler in the saddle.

T / F 9. When re-fusing a dead front, load break transformer, always energize the transformer from a remote location.

10. Before removing a bayonet fuse, an operator must:(a) Pull the take-off fuse.(b) Pull the relief valve.(c) Perform a voltage check.(d) All of these



11. When closing a normal open on a dead front, load break transformer, an operator requires the use of:(a) An 8 foot grip-all hotstick and an elbow puller

hotstick.(b) A modiewark and an elbow puller hotstick.(c) A grounding elbow and an 8 foot grip-all hotstick.(d) A modiewark and a grounding elbow.

T / F 12. When operating underground equipment, an operator must keep clear of energized parts.

T / F 13. An operator may isolate underground cables or transformers with the use of rubber gloves.

T / F 14. When placing the arc strangler in the saddle, be sure to cock the mechanism.

T / F 15. Always secure transformer doors.

T / F 16. Do not use a bayonet fuse to pick up load.

T / F 17. Always use a bayonet fuse to pick up load.

T / F 18. A bayonet fuse is not designed for fault closing.

19. A switching plan must include:(a) The date of switching, location of switching and

the number of customers affected.(b) The location of switching, the out and in switching

procedures and the number of customers affected.

(c) The out and in switching procedures, the number of customers affected and the date of switching.

(d) The location of switching, the out and in procedures and the date of switching.

T / F 20. Only the operator in charge has a copy of the switching plan; he will ensure it is carried out accordingly.

T / F 21. In a single-phase underground distribution loop system, a normal open prevents the entire loop from being out of power in the event of an underground fault.



Review Question Solutions

1. All of these

2. T

3. T

4. T

5. F

6. Two types of transformers.

7. F

8. F

9. T

10. Pull the relief valve.

11. An 8 foot grip-all hotstick and an elbow puller hotstick.

12. T

13. F

14. T

15. T

16. T

17. F

18. T

19. The location of switching, the out and in procedures andthe date of switching.

20. F

21. T

Documents

Single-Phase Underground Operating - SaskPower 3 Book 2/4. SINGLE-PHASE... · When operating in an underground single-phase system, an understanding of the causes of faults, and fault