INGLÉS unidad 7

Mark the correct statement: The direction of rotation of three-phase motors can be done by exchanging any two phases' connections. The failure of any phase of a three-phase motor is serious breakdown. DC motors are the most frequently used ones. a) and b) are true.

Please mark the incorrect answer: A contact has two types of contacts: power and control contacts. Control contacts are also called auxiliarycontacts. Power contacts feature higher breaking capacity. Auxiliary contacts have higher breaking capacity values that power contacts. All are incorrect.

In general, control circuit conductors: Have a 1.5 mm2 cross-section and are identified by red insulation. Have a 1.5 mm2 cross-section and are identified by black insulation for the phase conductor and blue insulation for the neutral conductor. Have a 1.5 mm2 cross-section and are identified by red insulation for the positive conductor and black insulation for the negative conductor. None.

Three-phase motors: Are larger than single-phase motors (being their rated power the same). Are equipped with a separate winding for each phase. Just have one direction of rotation, since changing this direction would imply dismantling the machine and exchanging one of its winding's polarity. All three answers above are true.

Single-phase motors: Are larger than three-phase motors (the rated power value being the same). Feature higher efficiency than three-phase motors. The change of their direction of rotation can be accomplished just by exchanging phase and neutral connections. All answers are true.

Indicate the right statement about the contactor coil: It is formed by a high-diameter cupper wire winding featuring a low number of turns. It is the part of the contactor that can be distance-controlled. A coil's three terminals are identified as A1, A2 y A3. None.

The device most frequently used in automation is: Common switches. Contactor. Diverter switch. None.

Mark the right statement about three-phase motors: Delta connection is recommended for the lowest rated voltage of an electric motor. Star connection is recommended for a motor's highest rated voltage. There is a device called contactor that is used for protecting motors from a phase failure. The direction of rotation of three-phase motors can be changed by exchanging any two phases'connections.

In automation circuit schemes: All elements belonging to a contactor are labelled KM. Every switching element (push-buttons, switches, etc.) are named S. All protection elements are identified with F. All are true.

Find out the correct statement: Electric motors are static machines that transform electric energy into mechanical energy. Electric motors are rotating machines which convert electric energy into mechanical energy. Electric motors are rotating machines which convert mechanical energy into electric energy. None.

A contactor comprises the following parts: Coil, electromagnet and electric contacts. Coil, pneumatic circuit and electric contacts. Coil, electromagnet and thermal elements.

Which of the following statements about the contactor is true? : It is robust and reliable, because it doesn't include any delicate mechanisms. It is a pneumatic device which can be distance-controlled for making or breaking currents. It is used for protecting motors upon failure of one phase. a) and c) are correct.

Please indicate which of the following statements about single-phase motors is wrong: They have two windings inside, one for starting and another one for steady state. The terminal box includes two terminals: the phase one and the neutral one. Four different terminals are included in the Terminal box, corresponding to the beginning and the endof phase and neutral windings, respectively. All are true.

Please indicate the right statement about the thermal relay: It is mainly used for motor starting automation. Its purpose is to project motors upon failure of a phase. all are false. all are true.

Please mark the false statement about three-phase motors: They include two windings, one of them for the motor starting and another one for the steady state ofthe motor. The terminal box includes six different terminals. They feature a winding for each phase. All are true.

A motor frame is connected to: It is connected through the metal screws, so no conductor is needed. The earthing electrode through the neutral conductor. The earthing electrode through the protective conductor. None.

According to the number of phases, electric motors can be: Single-phase. Two-phase. a) and c) are correct. All are correct.

In automation circuits based upon the use of contactors: Just the power scheme needs to be represented, since the control scheme is always the same. Power circuit conductors always have identical cross section to control circuit conductors'. Two different schemes must be drawn: power scheme and control scheme. None.

Which of the following statements about a contactor's electromagnet (magnetic circuit) is true? : The yoke and the hammer are the fixed parts, where the contactor coil is located. Some contactors feature a mechanical indicating element to inform on its operation status (on/off). It consists of two parts: the yoke and the hammer. None.

Please indicate which of the following statements on the thermal relay is false: It is an overload protection element situated in the power circuit. On detecting overload, it drives the auxiliary contacts which switch the whole circuit off and switch on asignalling element. Its operating principle is based upon bimetal strain. It is a protection element located in the control.