Does lowering voltage increase current?

There are two facets to this question.

First, on a distribution feeder, lowering the voltage a few percent with AdaptiVolt™ does not, in most cases, increase feeder current (depending on the load).  AdaptiVolt™ field testing actually shows a reduction in current for residential and commercial loads (see associated graphs).

For incandescent lighting or other not thermostatically controlled resistance devices (devices that follow the I²R rule), a drop in voltage reduces the current, the demand (kW) and reduced energy usage (kWh) over  time.  Ballasted lamps or those with magnetic ballasts become more efficient (lighting efficacy increases) as voltage is reduced within nameplate ratings.  This reduces demand (kW) of the lamp/fixture combination and reduces energy consumption (kWh.)

For thermostatically controlled electric resistance heating, hot water heating, electric clothes dryer or process furnace, reducing the voltage results in reduced demand (kW) for the individual unit itself.  The demand (kW) of the individual device is reduced based on I²R, but because the device is thermostatically controlled, the device "on" time will increase as a function of the voltage reduction to maintain the temperature set by the thermostat.  Energy consumption (kWh) of the resistance device will not be reduced over time.  On a utility distribution feeder, when the voltage is first reduced the demand (kW) will be reduced by some amount.  If there are a significant number of customers on the feeder with thermostatically controlled resistive devices the diversity factor increases meaning more devices will be "on" at the same time.  This causes the total demand (kW) on the feeder to increase from the level it went to just after the voltage reduction to some level below the level prior to the voltage reduction.  (See the associated graph.)  A mitigating factor that does reduce this effect is that many of these types of thermostatically controlled resistive devices have fans or motors associated with them, two examples being forced air electric furnaces and electric clothes dryers.  The motors operate more efficiently at the reduced voltage (see following paragraph) so that total kW and total kWh is reduced even with large numbers of these devices on a distribuiton feeder.

Many believe that reducing the input terminal voltage of an AC motor will increase the motor current and that running a motor at higher voltages is the best way to operate that motor.   This is only true if the motor is overloaded, that is it is required to provide a mechanical output that requires more horsepower or torque than the motor was designed to provide at 100% load.  Few persons would purposely select a motor that was under-sized for the application. Most electric motors, in residential use, in commerical HVAC or refrigerataion use or in industrial use have a factor of safety built in so that the required mechanical output is less than the motor is rated to provide.  In other words a motor is usually selected that will have a higher horsepower and torque rating that the mechanical load it has to drive.  When a motor is operating at any less than its rated mechanical output, reducing terminal voltage does reduce motor input kW, reduces the motor current, reduces the reactive power input requirement of the motor and improves the motor's operating power factor.  (see the associated graphs.)

The fact that motor efficiency increases when voltage is reduced a few percent with ANSI or CAN standards leads to improved air conditioning and refrigeration efficiency which further reduces current requirements on a distribution feeder.

Transformer core loss is reduced when input voltage is reduced.  This improves the efficiency of the transformer.  Solid state junction switching losses are also reduced when voltage at the junction is reduced improving the efficiency of the switched device.  This improves the efficiency of all equipment that uses either transformers or solid sate switching devices, e.g. computers, home electronics of all types, etc.

The simple fact of the matter is that reducing voltage a few percent with AdaptiVolt™ within ANSI or CAN standards saves energy (kWh), reduces overall demand (kW) andin most cases reduces distribution feeder current.  (see the graphs mentioned in the first paragraph.)

The second facet has to do with nominal distribution feeder voltage.  For example a 4 kV distribuiton circuit will have higher current levels than a 12 kV distribution circuit for the same load.  In this case, the two feeders will be designed with different transformers, and because the voltage is three times greater in one case, the current will be one third for the same load. Under AdaptiVolt™, we use whatever distribution voltage a utility has. We use the same transformers, etc. We lower the voltage a small amount (typically less than 5%) and the resultant energy usage along with current drops per the discussion above.