Single-Phase Underground Operating

Transcription

1 Single-Phase Underground Operating S T U D E N T M A N U A L March 31, 2005

2 2 STUDENT TRAINING MANUAL 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

3 SINGLE-PHASE UNDERGROUND OPERATING 3 Written test On-the-Job Evaluation On-the-Job Evaluation Written test On-the-Job Evaluation STUDENT RESOURCES Learning Steps Underground Tools module 1. 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.

4 4 STUDENT TRAINING MANUAL Lesson 1: Underground Faults Learning Objective:Identify fault situations in an underground distribution system. Learning Method:Self-learning + On-the-job Evaluation Method:Written test Introduction Operating is performed mainly at transformers where switching and fusing capabilities are readily accessible. Underground switching is often required due to underground faults. Some historical causes of faults 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, an understanding of the causes of faults, and fault locating are required skills. The knowledge of these basic operations can assist the operator in locating 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 the fault from the rest of the system. To do this, first determine which section of cable the fault has occurred at. The faulted cable is then isolated by using approved switching methods to temporarily restore power. Try to pinpoint the cable fault using fault locating devices. Specially trained personnel and equipment may be

5 SINGLE-PHASE UNDERGROUND OPERATING 5 required to find the fault. Finding Underground Faults (loop system) When a fault occurs on an underground system, the nature of the fault must be determined. If the take-off fuse has blown, check the transformer fault indicators to determine what section of the line has faulted. If the take-off fuse has not blown, perform a voltage check at the transformer in question to determine if the transformer fuse has blown. If the voltage on the secondary bushings is in accordance with the transformer nameplate ratings, the operator can suspect the secondary cable as the problem. If there is no voltage on the secondary bushings, remove the secondary cables from the transformer bushings and re-fuse the transformer. If the transformer fuse blows again with the secondary cables removed, the transformer must be replaced. If the transformer fuse holds with the secondary cables removed, the transformer is operational and the problem lies in the service cable.

6 6 STUDENT TRAINING MANUAL Lesson 2: Fusing Underground Live Front Transformers Learning Objective:Explain the procedure to fuse and operate a live front transformer. Learning Method:Self-learning + On-the-job Evaluation Method:Written test Introduction Live Front 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. The fuse in a live front transformer is located in the centre of the transformer buss assembly, and is identified by being slightly larger than the outer two arc stranglers. Reference For further information on live front transformers, refer to the Underground Tools module and Underground Apparatus module. ---Note--- When removing the fuse or arc strangler, it must be left in a visual location.

7 SINGLE-PHASE UNDERGROUND OPERATING 7 ---Note--- When placing the arc strangler in the saddle, be sure to cock the mechanism.! CAUTION Never leave an open arc strangler or fuse in its saddle as it is energized and may short out in the door. Remove it and store in an accessible location. STOP DANGER The buss assembly is still energized when the fuse is removed. Always maintain the recommended limits of approach when working around the buss assembly. Dead Front The following steps are guidelines to follow when operating in a dead front 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 the fuse is removed. Consult the Construction Standards manual for proper fuse size. When replacing the fuse cartridge, ensure the serrated end is tightened last. ---Note--- Upon replacing the bayonet fuse, ensure the collar is locked into place. ---Note--- Do not use the bayonet fuse to pick up the transformer load.

8 8 STUDENT TRAINING MANUAL! CAUTION The bayonet fuse is not designed for fault closing. Serious personal injury may result from internal transformer fault conditions, causing a rupture or the cover to blow off. Always energize the transformer from a remote location.

9 SINGLE-PHASE UNDERGROUND OPERATING 9 Lesson 3: Procedure to Fuse and Operate a Live-Front Transformer Learning Objective:Demonstrate the procedure to fuse and operate a live-front transformer. Learning Method:On-the-Job Demonstration and Practice Evaluation Method:On-the-Job Evaluation

10 10 STUDENT TRAINING MANUAL 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: 1. Open and block the transformer door. 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.

11 SINGLE-PHASE UNDERGROUND OPERATING 11 Lesson 4: Procedure to Fuse and Operate a Dead Front Transformer Learning Objective:Demonstrate the procedure to fuse and operate a dead front transformer. Learning Method:On-the-Job Demonstration and Practice Evaluation Method:On-the-Job Evaluation

12 12 STUDENT TRAINING MANUAL 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-all hotstick. 4. Push the bayonet fuse down and rotate the handle 90 degrees. 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 cartridge container. 3. Installation 1. Install the fuse into the fuse cartridge container and connect to the bayonet assembly using a wrench. 2. Insert the bayonet fuse assembly into the transformer fuse tube housing. 3. Turn the locking handle until the latch engages the tube housing. 4. Close and secure the transformer door.

13 SINGLE-PHASE UNDERGROUND OPERATING Use appropriate switching methods to energize the transformer from a remote location.

14 14 STUDENT TRAINING MANUAL Lesson 5: Switching Plan Learning Objective:Review the purpose and layout of a switching plan for underground switching. Learning Method:Self-learning + On-the-job Evaluation 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 while maintaining electrical service to as many customers as possible. The following 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

15 SINGLE-PHASE UNDERGROUND OPERATING 15 in procedures can be documented.! CAUTION Each worker must get a copy of this plan and follow it accordingly. The individual in charge will communicate all operations to the workers. Figure 1. Switching Plan

16 16 STUDENT TRAINING MANUAL Figure 2. Underground Single-Phase Loop Feed Underground Loop System On occasion, due to construction or maintenance, it is necessary to either isolate a cable, transformer or change a transformer bushing. These procedures usually involve moving a normal open in order to maintain electrical service.

17 SINGLE-PHASE UNDERGROUND OPERATING 17 In order to successfully complete the task and provide safe and reliable service, two steps are required: closing the normal open isolating underground apparatus Closing the Normal Open When underground maintenance or construction situations in a loop feed warrant a switching procedure, it will usually involve closing the normal open in order to maintain electrical service. ---Note--- The normal open is incorporated in an underground system to avoid large outages. STOP DANGER When operating underground equipment, always maintain the required clearances from energized parts.

18 18 STUDENT TRAINING MANUAL Lesson 6: Perform Switching in an Underground System Learning Objective:Demonstrate the procedure to perform switching in an underground system. Learning Method:On-the-Job Demonstration and Practice Evaluation Method:On-the-Job Evaluation

19 SINGLE-PHASE UNDERGROUND OPERATING 19 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 puller hotstick. 2. Open the transformer door. 3. Remove the arrestor or insulated cap in the H1B bushing with an elbow puller hotstick. 4. Remove the arrestor or insulated cap from the feedthrough with an elbow puller hotstick. 5. Remove the cable elbow from the feedthrough and install on the transformer H1B bushing. 6. Remove the arrestor or insulated cap ground leads with an 8 foot grip-all hotstick. 7. Remove the feedthrough with an 8 foot grip-all hotstick. 8. Remove the feedthrough ground lead. 9. Close and secure the transformer door. 2. Procedure to close the normal open in a live front load break transformer. 1. Clean an approved 8 foot grip-all hotstick 2. Open and block the transformer door. 3. Cock the arc strangler. 4. Install the arc strangler into the vacant saddle using an 8 foot grip-all hotstick. 5. Close the arc strangler into position.

20 20 STUDENT TRAINING MANUAL 6. Close and secure the transformer door. 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 an 8 foot grip-all hotstick. 5. Remove the faulted cable and install on the feedthrough using an elbow puller hotstick. 6. Install ground leads for the arrestors or insulated caps using an 8 foot grip-all hotstick. 7. Install arrestors or insulated caps on the feedthrough and transformer 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 an 8 foot grip-all hotstick. 2. Remove the faulted cable and install on the feedthrough using an elbow puller hotstick. 3. Install the ground leads for the arrestors or insulated caps using an 8 foot grip-all hotstick. 4. Install the arrestors or insulated caps on the feedthrough and transformer bushing using an elbow puller hotstick.

21 SINGLE-PHASE UNDERGROUND OPERATING Close and secure the transformer door. 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. 4. Open the transformer door. 5. Install the feedthrough ground lead using an 8 foot grip-all hotstick. 6. Install the feedthrough on the transformer parking stand using an 8 foot grip-all hotstick. 7. Remove the cable elbow from the H1B bushing and install on the feedthrough using an elbow puller hotstick. 8. Remove the cable elbow from the H1A bushing and install on the feedthrough using an elbow puller hotstick. 9. Close and secure the transformer door. 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 the appropriate 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 the bushing.

22 22 STUDENT TRAINING MANUAL 6. Install the cables on the feedthrough and drop them into the bottom of the transformer well.

23 SINGLE-PHASE UNDERGROUND OPERATING 23 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 to achieve 100%.

24 24 STUDENT TRAINING MANUAL 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

25 SINGLE-PHASE UNDERGROUND OPERATING 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 T / F T / F T / F T / F T / F T / F 12. When operating underground equipment, an operator must keep clear of energized parts. 13. An operator may isolate underground cables or transformers with the use of rubber gloves. 14. When placing the arc strangler in the saddle, be sure to cock the mechanism. 15. Always secure transformer doors. 16. Do not use a bayonet fuse to pick up load. 17. Always use a bayonet fuse to pick up load. 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 T / F 20. Only the operator in charge has a copy of the switching plan; he will ensure it is carried out accordingly. 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.

26 26 STUDENT TRAINING MANUAL 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 and the date of switching. 20. F 21. T