Power Load Controller and Alarm Device (PAD)

The Power load controller and Alarm Device (PAD) plugs in the AC power outlet and your appliance connects to the Device. Controller monitors continuously Voltage/Frequency and disconnects appliance to protect it when quality of electricity is not good for the specified appliance. Thus it protects your appliances from the fluctuations and bad quality of electricity. A red led on the Device designates the alarm and the disconnection of the appliance. With a rotary switch (in blue color in picture) the type of appliance connected to the controller Device is specified/programmed. Comes in 115V/60Hz and 230V/50Hz. Suggested for areas with problems in their electricity that had appliances destroyed in the past.

Power load controller and Alarm Device

When installed in most loads in isolated or autonomous power networks, load managment is achieved without extra wiring or communication between the controllers. Increases the efficiency on installations with renewable energy sources (Wind generators, photovoltaic panels ect.) and/or diesel generators. Manages the loads and stabilizes the power network.

The Controller is installed between a load and the power network. The Controller continuously monitors the Power Network (voltage signal) and extracts information about the state of the power network, at the exact point of the network that the Controller and the load are connected. The frequency is calculated . Based on this information, and the specified importance of the controlled load, the Controller decides what to do for its load: to connect it, disconnect it, keep it connected, or keep it disconnected. Its decision is based on (a) the voltage signal, (b) the voltage RMS value, (c) the frequency, (d) the recent history of the voltage signal, (e) the importance of the load, (f) the state of the load (ON/OFF) and (g) the time interval in that state.

The Controller can detect if the power network tends to become unstable. It can differentiate overloaded and underloaded conditions from generator trip and faults. Three levels where depicted to designate the Power Quality (PQ) level:

Good Voltage and Frequency in specified limits by utilities
Medium Voltage or Frequency slightly out of limits, but both in acceptable range.
Bad Voltage or Frequency out of limits.

The limits for acceptable ranges of Voltage and Frequency may vary according to the desirable behavior of the system. In addition, the voltage limits are set as a percentage of the nominal. The nominal is calculated by the controller itself often because the mean voltage varies from the first to the last loads on a distribution.

The Controller can detect even the slightest variations of the voltage and take action, since the design is based on sampling and processing by a microprocessor. Even though monitoring takes place continuously, action is taken at the end of every period.

When the power network tends to get unstable, load shedding is performed by the Controllers. Each Controller has a priority level assigned, based on the importance of its load. The priorities are implemented with the use of timers. When the Controller detects a frequency drop or a voltage drop then it starts a timer. When the timer expires the Controller considers that the network tends to be unstable and it will disconnect its load. The timers are counters of periods. Consider TdpM. to be the Time interval to Disconnect the load of Priority M. The time interval is set differently between the Controllers, according to the priority of their load and the type of problem detected on the network. The higher the priority is, the larger the time interval is set. The more severe the detected problem is, the smaller the time interval. For quick frequency drop the controller will act in one period. At least one period is needed for recognizing the type of problem. Lets consider a power network where the loads have priorities from 1 to N, where N is the lowest priority, and let Tdp1, Tdp2, …, TdpN be the time intervals for disconnecting the loads of these priorities respectively where:

Tdp1 > Tdp2 > _ > TdpN

This way lower priority loads will be disconnected before higher priority loads. After disconnection of some lower priority loads the network may recover and higher priority load disconnection may not be necessary.

When the power network recovers from an underfrequency or overloading, the loads will start to get reconnected. When the Controller detects that the voltage signal and the frequency have returned to nominal values it starts a timer. When the timer expires the Controller considers that the network has recovered and it will reconnect its load. Consider TcpM to be the Time interval to reConnect the load of Priority M. The time interval is set differently between the Controllers, according to the priority of their load. The higher the priority, the smaller the time interval. Lets consider the loads that have priorities from 1 to N, where N is the lowest priority, and let Tcp1, Tcp2, … ,TcpN be the time intervals for reconnecting the loads for these priorities respectively where:

Tcp1 < Tcp2< _ < TcpN

This way higher priority loads will be reconnected before lower priority loads. After reconnection of some higher priority loads the network may start to experience tends to get overloaded and then lower priority loads will remain disconnected. Each Controller has Tdp ,Tcp values in accordance to its priority.

The operation of the controller is based on states. A state machine with five states characterizes the functionality of the controller. The five states are: GetReady where load is OFF, Good where load is ON, Medium where load is ON, TempBad where load is ON, and Bad where load is OFF.

Acording to the program selected on the Controller with the blue rotary switch, the user can specify the (i) priority of the load on the controller, (ii)the voltage and frequency limits for the specification of the Power Quality, the time in (iii)Medium and (iv)Temporary bad states before the Controller disconnects the load.

A substantial percentage of Intelligent Controllers need to have been installed to loads to achieve distributed stabilization of the Power Network. When a small percentage of loads have Controllers installed, the effects of priorities are canceled and it becomes equivalent of hav ing no priorities. In this case all the loads with Controllers attached, will need to get disconnected and still stabilization is not achieved.

When all the loads on a site have controllers installed, and the main power goes off and a genetator starts up that cannot feed all the loads, the controllers automaticaly will disconnect the lower priority loads and the network will be stable.