The Virginia Electric and Power Co. yesterday proposed two experimental rate plans for some residential customers allowing them to pay less for electricity they use is so-called off-peak hours.

One plan, for about 9,000 selected customers who use $3,500 kilowatt hours of electricity or more per month in summer, would be mandatory.

The second category of consumers --720 and 3,490 kilowatt hours in the summer -- would be "invited, to volunteer." A kilowatt hour is the amount of electricity needed to power a 100-watt light bulb for 10 hours.

A Vepco announcement said the so-called "time-of-usage" plans were filed with the State Corporation Comcustomers who use 3,500 kilowatt hearings in mid-May on whether to adopt or modify the plans.

At the SCC's request, Vepco has been developing the time-of-usage plans for more than a year. The concept, under consideration by utility companies in other sections of the country, is a favorite of consumr organizations. It also is part of electricity rate reform legislation being considered in many states and Congress.

The mandatory proposal would levy a "basic monthly customer charge of $11.30," including the extra cost of special meters.

Other charges would be levied on a complicated rate schedule that Vepco itself hasn't calculated in detail, according to William W. Berry, a Vepco senior vice president.

Berry said, however, that during the past year Vepco had tested a sample of 600 customers drawn from all categories of usage. It discovered the time-of-usage plan resulted in savings of as much as 30 per cent for some customers and increases ranging up to 60 per cent for others.

He said the large increases tended to hit low-usage customers because they had "less to play with" -- that is, changing electricity usage from peak to off-peak hours.

For purposes of the experiment, peak hours are 10 a.m. to 10 p.m. and off-peak hours 10 p.m. to 10 a.m.

The idea is to find out when customers use electricity. Doing so requires special meters to register the time of day that, say, a television set is turned on and off.

If the SCC approves, Berry said, "After the new meters are installed, basic data will be collected and a customer education program conducted for about a year."

Berry said the basic idea of time-of-usage rates is to smooth out the peaks during the day when large demands are placed on generating equipment. This would reduce the need for extra generators, which now may lie idle 90 per cent of the time and work only during the hours of the day when, for example, many people are using air conditioners.