Impulse Phaser Historical Background
Since the first installations of underground cable, there has been a need to safely and accurately identify and phase cable. Early methods included systems that placed a pulsing signal on the conductor and identified using an exploring coil. Talking over the conductors using a telephone head set was another method employed. Although state of the art at that time, these techniques put the operator at risk because the conductors were not at ground potential. Consequently, if for any reason the conductors became energized, personal injury was inevitable.
Another practice for determining if a cable was de-energized was to "cut a window" in the lead sheath and the conductor shielding and touch the unshielded insulation with a sensitive voltage indicator. How could you be sure,if there was more than the one cable de-energized in the vault. This method always left a chance that the splicer may accidentally cut into the insulation resulting in a short circuit to the lead sheath.
Others say they rely on correct tagging of the cable circuits. How can you always be sure the tags are correct.
Due to the increased use of buried underground distribution cable, there is an increased need for a system to accurately and safely identify cables. All too frequently we hear where a splicer has accidentally cut into a cable that he "was sure" was de-energized.
In 1950, a safety conscious utility engineer realized there was a possibility for a potential fatal injury to occur using the above mentioned methods and set about to design a safer method for identifying and phasing high voltage cables.
The Impulse Phaser began service in early 1950 at that engineer's power company. A Patent for the instrument was issued in 1956.
The "keystone safety feature" of this new system was that the circuit had to be shorted and grounded in order for the instrument to function! Coupled with this safety feature was the ease of operation and accuracy.
There are two important points to consider:
1. Cable identification methods are used to verify a specific de-energized cable, possibly adjacent to energized cables.
2. Cable phasing methods usually involve two established conductors in a set of cables or terminations.
There are five general principles of using the IPD which are:
1. Never attempt to connect the Impulse Phaser to an energized cable regardless of the voltage!
2. Adjust the sensitivity control knob until a readable signal is obtained. Never advance the sensitivity control knob such that the indicating needle "pegs" either side of the meter! A half scale deflection is more than adequate.
3. Always face the labeled side of the clamp-on towards the cable end where the IPD transmitter is connected.
4. One of the most important safety features of using the IPD is that the instrument is designed to be used on a cable circuit that is shorted and grounded at the opposite end from where the transmitter is connected.
5. The clamp-on and detector will not be harmed if clamped around an energized cable. This can occur when trying to identify a single cable with other cables which cannot be de-energized.