It is not wise for commercial and industrial customers with CT-operated meters to interfere with them, since all utilities test these meters on a regular basis. An experienced meter reader or tester should be able to spot most of the common methods used to slow down a meter.
It is relatively easy to change the output of a CT and decrease
the meter registration. The bonus for the delinquent customer
is that not many utilities check CTs on a regular basis, so the risk of detection is small. Most utilities have some form of billing alarm preset to raise a query if a customer’s energy consumption decreases in an unusual manner. However, customer loads can vary for a variety of reasons, and the manpower is not always available to follow up on suspicions. A billing alarm is therefore not a reliable anti-theft device.
A clever thief will not cause a sudden drop in registration. He will do it a few percent at a time over many months, and end up saving, let us say, 50% of his bill. In the old days his disc meter might have been read by a human once a month, and his meter would have been tested anywhere from once every five years to once every three months, depending on his kVA rating. This offered a fair chance of his being caught.
One saving grace is that electronic meters are rapidly displacing disc meters for 3-phase metering; I have not heard of any major problems where customers have interfered with electronic meters. Of course, they are mostly read using AMR, and are thus not checked by humans – perhaps problems will appear in the years ahead?
If the customer modifies his CTs, however, there is practically no chance of his being caught. If his CTs are in error due to an installation mistake, they will probably stay in error for a long, long time. The thought of field testing CTs on a regular basis tends to dismay most utilities, which is understandable – meters are easy to test, CTs are much harder. Everyone knows that meters are involved in the payment cycle of customer to utility, so there are political reasons for making sure the utility does not cheat.
Only one in a thousand citizens knows about CTs, and CTs only apply to high revenue customers, so they stay below the political radar. This situation is changing where utilities are deregulated, and there are moves to force utilities to test CTs, whether they like it or not. That is not good news for honest customers, since faulty CTs short-change the utility, not the customer. (If anybody can tell me about a faulty or tampered CT that increased utility revenue, I am keen to record it.) But it is worse news for dishonest customers who play around with CTs to minimise payment.
Two Parts to the Problem
There are two parts to the CT problem. The first is testing and auditing them, so you know what you have. You believe you have accurate details on every metering CT in your system? That’s doubtful – the larger the utility, the more rogue CT installations you find when you go checking.
The second part is checking them every time the meter is tested; maybe less rigorously, just to make sure they have not been tampered with or suffered some other partial failure. CTs that fail completely are easily noticed, but partial failure is possible and not easy to find.
You say that looks like a lot of dollars for the equipment and labour cost? Well, if you plan to test them with direct injection, you are correct. But if testing to 0.1% is good enough, there are ways to do it with low-cost equipment and minimum time. You can even test live CTs as well as dead ones, both HV and LV types.
The CT problem that is really hard to beat is the tampering done by remotely operated relay. When the customer knows that his meter and CTs are about to be checked, he throws the switch. Only a close visual inspection of the CTs and the secondary loop will catch that one. If you run a software program to check his energy profile on the day before and the day after the meter/CT test, it might reveal a suspicious trend, but the customer could retaliate with more intelligent use of the switch if he knows you have that program. Eradicating theft is a never-ending story.