How to keep a room smoke-free?

Application description

Here we describe how a frequency inverter can be connected and configured to ventilate a room and keep it smoke-free in case of fire or extreme smoke development. In normal circumstances, the fan is controlled via the potentiometer or the motor runs at a fixed speed. If an error occurs, the motor will stop. In case of fire or smoke development, the motor will keep on running, no matter what error occurs. In this emergency situation, the frequency inverter will keep the motor running as long as possible, while ignoring all errors. This operation mode is called 'Fire mode'.

Connections

The wiring diagram shows an example where the supply voltage (3x 400 VAC in this example) and the AC motor are connected to the frequency inverter. On top of that, the inputs of the frequency inverter are connected to the external switches A and B, to the fire alarm detector and to the potentiometer.

Switches A and B can be used for following commands:

Switch A: start/stop command for the motor. It is connected to DI1. When switch A is open (DI = 0), the motor will stop. When switch A is closed (DI1 = 1), the motor will run. If the motor should always run, switch A must always remain closed. A wire bridge can be used to obtain this. In case a start/stop command is desired, the SW contacts of the potentiometer can be used (to be connected to DI1). DI1 corresponds to terminal 2 of the frequency inverter's input terminal block.
Switch B: speed selection in normal mode. It is connected to DI2. When the motor is running in normal mode (no fire alarm), the speed can either be set by the potentiometer (type SDP-X10K-NA, connected to AI1) or either be a predefined value (P-23 REF). When input 2 is low (switch B is open), the motor will run at the predefined value. When input 2 is high (switch B is closed), the motor speed can be set by the potentiometer. DI2 corresponds to terminal 3 of the frequency inverter's input terminal block.
The Fire alarm detector is connected to DI3: When DI3 is activated, the frequency inverter goes into 'Fire mode' and the frequency inverter will ignore all errors that would stop the motor in normal operation. DI3 corresponds to terminal 4 of the frequency inverter's input terminal block.
The potentiometer is connected to AI1: Any potentiometer with a 0-10 Kohm output value can be used. When digital input 2 is high (switch B is closed), the motor speed can be set by the potentiometer. AI1 corresponds to terminals 5, 6 and 7 of the frequency inverter's input terminal block.

Fire mode

The Fire mode function in frequency inverters is designed to ensure continuous operation of the frequency inverter in emergency conditions until it is no longer capable of sustaining operation. The Fire Mode input may be a normally open (Close to Activate Fire Mode) or Normally Closed (Open to Activate Fire Mode) according to the setting of P-30 Index 2. In addition, the input may be momentary or maintained type, selected by P-30 Index 3. This input may be linked to a fire control system to allow maintained operation in emergency conditions, e.g. to clear smoke or maintain air quality within that building.

Fire Mode disables the following protection features in the frequency inverter to make sure that the motor keeps on running as long as possible in emergency conditions:

O-t (Heat-sink Over-Temperature), U-t (Drive Under Temperature), Th-FLt (Faulty Thermistor on Heat-sink), E-trip (External Trip), 4-20 F (4-20mA fault), Ph-Ib (Phase Imbalance), P-Loss (Input Phase Loss Trip), SC-trp (Communications Loss Trip), I.t-trp (Accumulated overload Trip).

Ignoring these error messages can lead to permanent motor damage. Therefore, it is recommended to only use the 'Fire mode' function in emergency situations.

Configuration of the frequency inverter

Starting from the default settings, in addition to the motor parameters (depending on the type of AC motor you are using), the following parameters also need to be changed to obtain the above described functionality:

Parameter 14: must have value 101 - this gives you access to the extended menu (all parameters higher than 14)
Parameter 15: must have value 15 - this changes the functionality of the frequency inverter's inputs as follows:

Parameter 23: set here the desired motor speed in normal operation in [Hz]. Keep in mind that the desired motor speed must be in between the minimum Frequency (defined in parameter 2) and the maximum frequency (defined in parameter 1).

Further settings can be made if desired. For example, the acceleration time (P-03) or deceleration time (P-04) of the motor can be changed, maximum (P-01) and minimum speed (P-02), etc.