Optimization of Max Demand Control using L&T E&A 4420 series DPM

Max Demand Controller (L&T E&A 6000 series) is used to ensure that contract demand is never crossed, and penalty is avoided. The meter is time synchronised with the EB meter and configured to ensure that demand never crosses the threshold limits. 4 relay outputs are available for proper load control.

However, there are a couple of energy guzzler feeders in downstream where users would require indication whenever there is an abnormal rise in demand. Here Load manager L&T E&A’s 4420 series with MD parameter and 2 digital relay outputs helps the users to get indication whenever the demand crosses the set limits.

There are two types of demand calculation methods – Block window and Sliding window. Since 4420 series does not have real time clock therefore sliding demand is the best method for demand indication. This window slides every 1 second (update time) for the window period of 15 or 30 mins (site selectable). But at the end of the demand period it doesn't return to zero. This is the better method of measurement for the fluctuating loads. The graphical representation of sliding window is shown above.

Sliding method for demand calculation with step method for control can be used with 2 threshold limits. Two threshold limits of High limit 1 and 2 can be set as follows:

Relay 1:- High Limit 1 can be set from 1% to 100% of Full scale*

Relay 2:- High Limit 2 can be set from 50% to 99% of High limit 1

Low limit (for reset) can be set from 50% to 99% of High limit 2 for reset

*Full scale is 1.732 * PT (primary) * CT (primary) / 1000

An example with below image for a feeder with demand profile on sliding basis is shown in figure below.

Therefore, if running demand breaches High limit 1 then Relay 1 (NO) would be activated. If High limit 2 threshold is crossed, then Relay 2 (NO) would be activated. The relays will be reset when demand comes below the low limit value. The output of these relays can be given to alarm or contactor coil**.

The highest running demand will be recorded as the max demand till it is reset.

L&T E&A’s 4420/ 4430 series with 2 relay outputs empowers the user to take steps to keep energy consumption on track.

Applications

Few applications are listed below though not exhaustive:

1. Monitor voltage variations at say 1 or 5 minute interval at incomer level to understand the voltage fluctuations from transformers.
2. Monitor energy consumption at 15 minutes interval.
3. Monitor running demand at every 15 minutes. Based on this data, the customer can analyse the existing contract demand levels. If the contract demand levels can be reduced by 5-10% then customer can save tremendously over a long term.
4. Log max demand at every 15 or 30 min interval to analyse demand trend patterns.
5. 5000 series meters with analog inputs like temperature can be logged inside the meter and analysed for further actionable.
6. Monitor PF levels at every 1 hour interval.
7. Monitor K factor levels at Incomer level. (refer Watt File 4 for more details on K factor)

The next level approach will be to get a comprehensive report, trend analysis, email reports and analytics using SmartComm EMS.