Transfer switches

Optional standby power systems are for systems whose failure could cause effects such as damage to process equipment, interruption of manufacturing processes, loss of airflow to maintain cleanliness conditions, etc. Although not required by code, process engineers may want selected production equipment on optional standby power. Loads which are not related to life safety, yet are desired to be connected to the emergency power system, must be separated and controlled by their own transfer switches. The nonlife-safety loads must be able to be shed, if necessary, due to a generator malfunction. 

In general, automatic transfer switches are provided for code-required emergency loads, and manual transfer switches are provided to change from a main to a standby fen or pump, or to change from a normal to redundant power source. (See Fig. 4.) 

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An open-loop system positions the manipulated variable either manually or on a programmed basis, without using any process measurements. This operation is acceptable for well-defined processes without disturbances. An automanual transfer switch is provided to allow manual adjustment of the manipulated variable in case the process or the control system is not performing satisfac torily. 

A third alternative is to rate the transformer in-feeds for single supplies but to arrange for automatic switching of the bus section and two incomers in the event of loss of supply to one section. A rapid transfer switching to the remaining supply in the event of loss of single supply can prevent the total loss of motor loads. In such a situation, the effect of the current taken by motors to which the supply has been restored must be taken into account. 

Takakusa H, Kikuchi K, Urano Y, Kojima H, Nagano T (2003) A novel design method of ratiometric fluorescent probes based on fluorescence resonance energy transfer switching by spectral overlap integral. Chemistry 9 1479-1485... 

The manual-automatic (M-A) transfer switch, immediately below the output meter, selects operating mode of the controller. 

A manual output adjust knob, in the center of the M-A transfer switch, varies the controller output signal in manual mode of operation. The knob is rotated clockwise to increase the signal and counterclockwise to decrease the signal. 

The M-A transfer switch has five positions that alter the mode of operation. The indication is provided by the deviation meter. 

AUTO. This is the normal position of the M-A transfer switch. It places the controller in the automatic mode of operation. Also, the deviation meter indicates any deviation between controlled variable and setpoint. 

To ensure a bumpless transfer from manual to automatic, the manual output signal, indicated by the output meter, is adjusted to match the controlled variable value to setpoint. This will be indicated by no deflection of the deviation meter. Once matched, the M-A transfer switch can be switched from manual (MAN) to automatic (AUTO) control. 

The manual-automatic transfer switch is a five position switch that alters the mode of operation. 

Start-up of the exhaust ventilation system and critical equipment must be sequenced to prevent a hazardous condition. In addition, the starting of the supply air handling unit and the exhaust fan services each room shall initiate simultaneously to avoid placing the room under positive pressure. Automatic transfer switching will be used. 

As a rule, the sequence in which the columns are placed in a column-switching system has a marked effect on the results of a 2D separation. The final choice is dictated by the specific separation objectives. When subsequent fraction cuts have to be performed on the effluent from the first dimension, the column with a higher peak capacity should be placed into the first-dimension system and the flow rate should be matched to the fraction transfer switching period. The fractions transferred to the second-dimension column should be completely eluted before the subsequent fraction is transferred from the first to the second dimension. To increase the peak capacity in the first dimension, gradient elution is preferred to isocratic conditions. 

Gas Chromatographic Oven. Aerograph Hy-FI, Wilkens model 550, equipped with electron capture detector, isothermal proportional controller, differential flow controller, and detector transfer switch. By using the detector transfer switch, this additional oven permits the use of two different columns without cooling which would otherwise be required to change columns. 

Apply an input signal to the loop controller equivalent to 50% of the instrument range and adjust the output of the manual pneumatic regulator to 50%. Adjust the loop controller setpoint to 50% and, by switching the auto/manual transfer switch, check for bumpless transfer. Using the manufacturer s instructions, adjust where necessary until a satisfactory bumpless transfer is achieved. 

Important loads can be connected to redundant feeder circuit breakers, one on each side of the double-ended switchgear, by connecting the load sides of the circuit breakers together with a feeder cable. This approach should be used with caution. Another approach is to connect the redundant feeder circuit breakers to a time-delayed automatic transfer switch. 

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