Definition: A maximum demand indicator measures the highest amount of power required by a consumer over a specific time interval. It is designed to track both base and peak loads but does not record sudden short-circuit currents or the high inrush current during motor startup. This device is used to monitor and record power consumption over defined periods, helping in efficient energy management.
The maximum demand indicators are classified into four types:
- Recording Demand Indicator – Continuously records the power demand over a specific period.
- Average Demand Indicator – Measures and displays the average power demand over a given time interval.
- Thermal Type Maximum Demand Indicator – Uses thermal elements to measure and indicate maximum demand based on heat generation.
- Digital Maximum Demand Indicator – A modern, electronic version that accurately records and displays power demand using digital technology.
Construction of Maximum Demand Indicator
The maximum demand indicator consists of five main components, each playing a crucial role in measuring and displaying the maximum power demand:
- Dial Connected to the Moving System – The dial is calibrated to show the power demand readings and is linked to the internal moving system for accurate measurement.
- Pointer – This indicates the highest power demand recorded within a specific period.
- Reset Device – Used to manually or automatically reset the indicator after a certain time interval.
- Fraction Device – Helps in measuring fractional increments of power demand for greater accuracy.
- Indicating Pin – Marks the peak demand point on the dial, ensuring easy readability of the maximum demand value.
Average Demand Indicator
The average demand indicator is an integral part of an energy meter. It works alongside the energy meter to measure both the total power consumed and the maximum power demand over a specific time interval. This device helps in monitoring power usage trends and optimizing energy consumption.
The Merz-Price Maximum Demand Indicator is also known as the Average Demand Indicator because it measures the average power consumption over a specific time interval. Merz-Price Maximum Demand Indicator diagram is shown below.
The average demand indicator features a complex speed dial mechanism, which ensures precise measurement by calculating the average power demand over a predefined period. This mechanism allows for an accurate assessment of power usage, aiding in efficient load management and preventing excessive demand charges.
The pin drive moves the dial forward for a short duration, typically around half an hour. During this interval, the total power consumed is displayed on the dial. The instrument features a cam mechanism, which is controlled by timing gears. This cam resets the pointer back to the zero position after each measurement cycle.
The pointer records the total power consumed by the load within that specific time frame. In the following interval, the pin drive moves forward again. However, the pointer will advance only if the power consumption exceeds the previous recorded value. This ensures that the indicator captures the highest power demand within a given period, helping consumers monitor peak loads effectively.
The formula to calculate the average maximum demand is:
Average Maximum Demand=Total Energy Consumed (kWh)/Time Period (Hours)
The maximum demand meter can measure power in terms of kVArh (kilovolt-ampere reactive hours) or kVAh (kilovolt-ampere hours). This is achieved by incorporating an appropriate meter designed to calculate these specific quantities. By using such meters, consumers can accurately monitor their power usage patterns and optimize energy consumption accordingly.
Advantages of Maximum Demand Indicator
- Provides high accuracy in measuring maximum demand.
- Features a uniform scale for precise readings.
- Helps in optimizing power usage by identifying peak demand periods.
- Aids in cost reduction by preventing unnecessary overloading and penalties.
Disadvantages of Maximum Demand Indicator
- The use of a gearing mechanism makes the construction complicated and increases the cost.
- Requires regular maintenance to ensure accuracy and proper functioning.
- Cannot detect sudden load fluctuations such as short circuits or motor starting currents.
- Limited adaptability to modern digital power monitoring systems.
Read Next: