Motors operation

Nuclear Radiation Effects. Components of a nuclear reactor system that require lubrication include control-rod drives, coolant circulating pumps or compressors, motor-operated valves, and fuel handling devices, and, of course, are exposed to varying amounts of ionising (14). 

For an overload of 25%, a class B motor, operating at an ambient temperature of 45 C, the relay corresponding to 10% over temperature rise can be set to trip as follows ... 

Tbe use of special motors was more relevant until the 1980s. when solid-state technology was still in its infancy and wa.s not so widely applied. With the advent of static drives, as discus.sed in Sections 6.2-6.4, the use of standard motors is gradually becoming more common for all these applications. The drive it.self can alter the supply parameters to the required level to make a standard motor operate and perform within desired parameters, besides conserving energy. The purpose of describing a few of these applications is only to indicate their non-standard features, where a standard motor with normal controls may not be able to perform the required duties. 

Air-filled The latest practice is to keep the housing empty. This arrangement is found to be economical and the motor operates at higher efficiency. 

It is for this reason that rotors, as standard practice, are designed to withstand a much higher temperature of the order of 400 50°C in LT motors and 300-350°C in HT motors, compared to a too-low temperature of the stator. This temperature is such that for almost all motor operating conditions meticulous protection of the stator would also protect the rotor. It is also ob.served that rotor failures are therefore rare compared to stator failures. 

These receive power from the PCC and feed it to a number of load points, the majority of them being motors operating on an electrical installation or a process line. 

Pony motors are additional, small motors connected to the same fan shaft. They are typically about 1/4 the size of the full size motor. Pony motors do not lend themselves to gear box applications and are, therefore, primarily applied to belt drive applications. The big motor operates when full capacity is required and the small motor simply free wheels. At reduced capacity, the small motor operates and the big motor spins freely. 

Fail-safe Design features that provide for the maintenanee of safe operating eonditions in the event of a malfunetioning eontrol deviee or an interruption of an energy souree (e.g., direetion of failure of a motor-operated valve on loss of motor power). 

Motor operator faiks to respond Flow blockage No flow to header Redundant train ... 

Each independent and dependent operator has two aspects 1) Operation represents a component requiring actuation. For example, a motor-operated valve, is represented as a Type 6 operator since the valve needs both an input (flow) and an actuation (electric power) to pass the flow... 

For example, Table 5.1-3. shows that a motor-operated valve can fail in several ways. 

Table 5.1-3 Motor-Operated Valve Failure Modes...

Failure of power or controls to the valve (generally related to the seismic capacity of the cable trays, control room, and emergency power). These failure modes are analyzed as failures of separate systems linked to the equipment since they are not related to the specific piece of equipment (i.e., a motor-operated valve) and are common to all active equipment. 

The fault tree (Figure 7.4-1) has "Pre.ssure Tank Rupture" as the top event (gate G1). This may result from random failure of the tank under load (BEl), OR the gate G2, "Tank ruptures due to overpressure" which is made of BE6 "Relief valve fails to open" AND G3, "Pump motor operates too long." This is made of BE2, "Timer contacts fail to open," AND G4, "Negative feedback loop inactive" which is composed of BE3, "Pressure gauge stuck," OR BE4, "Operator fails to open switch," OR "BE5, "Switch fails to open,"... 

Primarily focuses on pumps, motor-operated 121, valves, and breakers... 

In the CCPS taxonomy, where the equipment boundary for a motor-operated pump includes the motor, shaft, seals, casing, impeller and the circuit breaker, then the demand-related failure is attributed to the pump. 

Similarly, an electric motor can use electricity that costs more than the motor during a year of continuous operation. Even if the motor is in perfect condition, it may be cost effective to replace it with a new motor that is a few percentage points more efficient at converting electricity into work. In many applications, however, an electric motor operates only a few hours per year. In such cases, the cost of the electricity is negligible relative to the cost of a new motor, so that even a large gain in energy efficiency is not worth the cost. 

Aside from the efficiency of the motor itself, energy efficiency is very dependent upon proper sizing. While the efficiency of a motor is fairly constant from full load down to half load, when a motor operates at less than 40 percent of its full load, efficiency drops considerably, since magnetic, friction, and windage losses remain fairly constant regardless of the load. Moreover, the power factor drops continuously as... 

The synchronous motor starts and accelerates the connected load like an induction motor, and is designed to give the hest possible induction-motor operation during starting, consistent with good synchronous-motor performance. 

Circuits that carry AC current employing two, three, or more sinusoidal potentials are C2 ed polyphase circuits. Polyphase circuits provide for more efficient generation and transmission of power than single-phase circuits. Power in a three- (or more) phase circuit is constant rather than pulsating like the single-phase circuit. As a result, three-phase motors operate more efficiently than single-phase motors. 

Shunt-Wound Motors. These motors operate at approximately constant speed regardless of variations in load when connected to a constant supply voltage and with fixed field excitation. Maximum decrease in speed as load varies from no load to full load is about 10-12%. 

Efficient use of electric motors requires appropriate control systems. Typical control systems for AC and DC electric motor operations are now discussed [ 10]. 

These AC drive systems require the inverters to operate with either low-slip induction motors or reluctance-type synchronous-induction motors.. Such systems are u.sed where DC commutator motors are not acceptable. Examples of such applications are motor operations in hazardous atmospheres and high motor velocities. 

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