The connected load is the sum of the continuous ratings of all the equipment connected to the supply system.
In other words, the connected load is the sum of all the nameplate ratings of the equipment within the consumer installation.
Calculation of Connected Load
Here is an example to illustrate what is the connected load on a power station and how it is calculated. Consider a power station supplying loads to 1000 consumers. In every consumer’s home, there is certain equipment installed. “Connected load” of a consumer is the sum of the continuous ratings of all the equipment of the consumer’s premises.
For example, if each consumer of the power station has the following connections
- Five 100-watt lamps
- Two 60 watt fans
- Power socket point of 500 watts
Then the connected load of one consumer is 5×100 + 2×60 + 500 = 1120 watts.
This is the CL of one consumer. Similarly, every consumer has their own connected load depending on the electrical equipment used in their house.
When you add up the connected loads of all the consumers, you get the connected load for the power station.
CL for the power station = 1120 × 1000 = 1120000 W = 1120 kW.
Connected Load vs Demand Load (Maximum Demand)
As we discussed above the CL is the sum of all the loads that are connected to the power system as a whole.
The maximum demand or peak load of a power station can be found in the load curve is defined as the greatest of all the demands which have occurred in the power station during a given period.
The figure below shows the maximum demand in a daily load curve.
The power plant supplies power to all the loads connected to it. This does not necessarily mean that they will all receive power together. For example, you might switch off the lighting loads during the daytime. During the night, certain factory loads might be disconnected. Occasionally, some motors will turn on and off. When the long travel motor of the crane is running, the hoist motor is switched off. Therefore, in practice, the total load on at any one time is less than the total connected load.
Imagine you were an electric company serving 1000 homes with only a 3000 watt electric oven in each house. Your CL would be 3,000,000 watts.
In reality, there may never be a time when all homes use heaters at the same time. Let’s say that only 500 homes use heaters all at the same time. The reason for this is what we call load diversity, or load factor. This would result in a demand load (maximum demand) of 1,500,000 watts. In that case, you only need to design your system for half the value of the connected load.
Many high-wattage appliances (such as toasters) have a very low load factor. Other appliances (electric heat) can have very large load factors at times (in very cold weather).
Ultimately, there are a great variety of appliance types, each with its own load factor, and the utility has to worry about only the aggregate of ALL connected loads.
Demand Factor is the ratio of maximum demand on the power station to its connected load.
Demand factor = Maximum demand/Connected load
The value of the demand factor is usually less than 1. It is expected because the maximum demand (peak load) on the power station is generally less than the CL.
If the maximum demand on the power station is 80 MW and the connected load is 100 MW, then the demand factor = 80/100 = 0·8.
The knowledge of the demand factor is vital in determining the capacity of the plant equipment.