Field Situation #2 - Installation of a single phase transformer.
Field Situation #1: Installation of a three-phase transformer. There is a three-phase circuit installed in an Industrial Park. A new building under construction requires the installation of a three-phase transformer.|
The new transformer is set. The three cables from the new transformer have been installed in a trench intersecting an existing, operating three-phase circuit. Exposed in this splicing location is the existing operating three-phase circuit and the three new cables from the new transformer.
Procedure 1: Identify phases in the "existing" three-phase circuit at the splice location.
1. De-energize and ground the existing three phase circuit.
2. At #1 transformer: Place the incoming cable elbows from #2 transformer onto feed-thrus. Install pre-molded insulated end caps onto the transformer bushings. Check open feed-thru bushings for potential. Using grounding elbows, install the grounding elbows into the open side of the feed-thrus. Now these three cable ends are shorted and grounded.
3. At transformer #2: Place the outgoing cable elbows to #1 transformer onto feed-thrus. Check feed-thru bushings for potential. Using grounding elbows, install the grounding elbows into the open side of the feed-thrus. Now these three cable ends are shorted and grounded.
4. At transformer #1: Disconnect the grounding elbow ground clamps from the system ground, but leave the grounding elbows in the feed-thrus. Keep these three grounding elbow ground clamps clear of ground. Connect the RED lead of the IPD transmitter to the "A" phase cable. Connect the YELLOW lead to the "B" phase cable. No connection is made to "C" phase.
5. Turn the IPD transmitter on. The amber lamp should begin to "blink" indicating that a signal can be obtained on the cables in the trench because the opposite end of the circuit is shorted and grounded.
6. At the splice location: With the clamp-on connected to the detector, depress the "ON" button completely and center the indicating needle by adjusting the "BALANCE" control knob. Adjust the "SENSITIVITY" control knob to "5".
Note: In a classroom situation, using shielded wire leads to demonstrate this operations, set the sensitivity control knob to the lowest possible setting.
7. Begin to clamp over the existing cables and identify the three phases . Remember to hold the clamp-on with the identified side of the clamp-on facing towards the end of the circuit where the IPD transmitter is connected.
Note: If there are more than three cables in the trench, and the cables are randomly laid, it is prudent to remove the "RED" lead from "A" phase at the transformer and connect it to the "C" phase grounding elbow cable to identify it at the splice location.
10. Identify and permanently mark the cables for future reference, then return to transformer #1, turn off the IPD and remove the "RED" and "YELLOW" leads from the grounding elbow cables. Re-connect the grounding elbow cables to the system ground.
Procedure 2: Identify phases of the new cable ends at the splice location.
1. Expose the three new cable conductors at the trench and short and ground the three conductors together using a grounding harness. Make good connections.
2. Return to the new transformer with the IPD transmitter. Install the transformer elbows onto feed-thrus and use grounding elbows or other means to connect the "RED" lead of the IPD transmitter to the "A" phase elbow and the "YELLOW" lead to the "B" phase elbow. Turn the IPD transmitter on. The amber lamp should begin to "blink".
3. Identify the new cable phases in the same manner as the existing circuit was previously identified.
Field Situation 2: Installation of a single-phase transformer. A new single phase transformer that will be loop fed from an existing three-phase cable circuit has been installed and must be connected to the "B" phase of an existing three-phase cable circuit.
A hole has been dug exposing the existing three- phase cable circuit. The new cables from the single phase transformer have also been trenched to this location.
1. Identify "B" phase of the existing three-phase circuit.
Procedure 1: Identify phases of the new cable ends.
1. Since it is an operating single-phase loop feed circuit, it will be necessary to close the open point in the loop, and isolate the cable between the two transformers. If the three-phase circuit is feeding all single phase transformers, such as would be the case in servicing a residential subdivision, then it would only be necessary to de-energize "B" phase. The two remaining cables in the trench would remain energized. Depending on company work rules, these two energized cables can be covered with a rubber blanket for safety while working on the "B" phase cable.
2.Safely denergize and isolate "B" phase cables on feed thrus with grounding elbows in transformers #1 and #2.
3. At transformer #1: Remove the grounding elbow cable leads from the system ground and attach the "RED" lead of the IPD transmitter to the "B" phase grounding elbow cable lead. Keep this connection clear of ground.
4. Attach the "YELLOW" lead of the transmitter to the system ground (i.e. concentric neutrals, transformer grounds, ground rods, etc.).
5. Turn the IPD transmitter on. The amber lamp should begin to "blink". This indicates that the "A" or "RED" phase signal is traveling through the cable you want to identify. The "B" or "YELLOW" phase signal is returning over all of the grounds and shields back to the IPD transmitter.
6. At the splice location: With the clamp-on connected to the detector, depress the "ON" button completely and center the indicating needle by adjusting the "BALANCE" control knob. Adjust the "SENSITIVITY" control knob to "5". Begin to clamp around the various cables until you find a conductor which gives a deflection to the "A" or "RED" side of the meter. This indication can not, and will not be on any other cable. The "RED" signal cable is the cable into which you will splice the two cables from the new single phase transformer. Return to the transformer and remove the IPD transmitter leads and replace the grounds. Leave the transmitter here for further use.
Note: During an indoor demonstration to show how an individual cable of a group of cables can be identified you use short pieces of shielded cable, The "A" or "RED" phase signal is traveling down the conductor which you are trying to identify and the return pulse is divided between all the neutral conductors. Consequently, in this type of demonstration, there will be a weak "B" or "YELLOW" phase signal on the two remaining cables. Therefore, one cable will give an "A" or "RED" signal and the other cables will give a "B" or "YELLOW" signal. The cable you want to work on is the cable with the "A" or "RED" signal. In field applications, you will probably never see the "B" or "YELLOW" signal due to the multiple return ground paths available.
7. The final safety check, after the cables have been identified and the phases marked, is to spear or sever the cables with a remote, insulated system.
NOTE: Some utility's interpretation of OSHA rules and even their own safety rules, requires further preparation of the cable before cutting. Always follow approved practices for your utility.
8. Before cutting the cable, the concentric neutral continuity must be maintained for safety reasons. This is accomplished by installing some type of jumper cable having equal or greater conductivity than the concentric neutral.
This requires the careful removal of the jacket from the cable for the distance required to complete a splice plus the room required by the jumping device.
9. Return to the transformer with the IPD transmitter and remove the grounds re-connect the "RED" lead to the de-energized "B" phase and turn the Impulse Phaser on. The amber lamp should begin to "blink".
10. Return to the splicing location and half way between the neutral jumper connections, using a pair of diagonal pliers, begin to cut the concentric neutral wires.
Note: When this operation is required for single phase identification, this operation will provide another opportunity to check to be sure that you are working on the correct cable.
We previously discussed identifying a single phase circuit, and that the return signal travels across all conductive neutral and ground paths returning to the Impulse Phaser, including the concentric neutral of the cable you identified with a "RED" signal. As you begin to cut each concentric neutral wire, install the clamp-on with the identified side facing toward the IPD transmitter location. When clamped over the cable with the remaining concentric wire the signal will be to the "RED" side of the meter. When clamped over the jumper cable you will get a "YELLOW" signal and this signal will increase as more wires are cut. These indications further prove that this is the cable you want to work on.
11. Return to the transformer and IPD transmitter when all concentric neutral wires are cut and remove the IPD transmitter leads and replace the grounds.
12. Return to the splicing point and you are now ready to sever the cable with the remote cutter, but, before cutting, observing good safety practices, connect a ground between the cutter blade and the jumper cable.
If there is ever a question in your mind as to whether the cable you have identified is truly the cable you want to cut, the operations described above should remove any doubt.