Electrician basics and ppt
Introduction: the multimeter should be connected in series in the circuit to be measured when measuring current, and the multimeter should be connected in parallel in the circuit to be measured when measuring voltage. Here is the basic knowledge of electrician and ppt that I brought for you, I hope it will help you.
First, the general part
1, what is called circuit?
The path through which an electric current travels is called a circuit. Circuits are generally made up of a power supply, a load, and connecting parts (wires, switches, fuses).
2. What is meant by power?
A power supply is a device that converts non-electrical energy into electrical energy.
3, what is called load?
A load is a device that takes electrical energy, i.e., a device that uses electricity.
The connection part is used to connect the power supply and the load, forming the intermediate link of the current path, is used to transport, distribution and control of electrical energy.
4. What is the basic concept of current?
Regular directional flow of charge, the formation of electric current, the customary direction of positive charge movement for the actual direction of the current. A circuit in which the direction of current is constant is called a DC circuit.
The amount of electricity that passes through any cross-section of a conductor in a unit of time is called the current (intensity), and is represented by the symbol I. The current is the amount of electricity that passes through a conductor in a unit of time.
The unit of current (strength) is Ampere (A), the unit of large current is commonly used kiloampere (KA), the unit of small current is commonly used milliampere (mA), microampere (μA) said.
1KA=1000A
1A=1000 mA
1 mA=1000μA
5, What are the basic properties of voltage?
1) The voltage between two points has a uniquely determined value.
2) The voltage between two points is related only to the position of the two points and not to the path of charge movement.
3) There are positive and negative voltages, which are related to the direction of the reference voltage of the sign.
4) The sum of the voltages of the segments is constant at zero when traveling one revolution along any closed loop in the circuit.
Voltage is measured in volts (V) and, depending on the need, in kilovolts (KV), millivolts (mV) and microvolts (μV).
1KV=1000V
1V=1000 mV
1mV=1000μV
6, What is the concept of resistance?
The ability of the conductor to block the current is called resistance, with the symbol R, when the voltage is 1 volt, the current is 1 ampere, the resistance of the conductor that is 1 ohm (Ω), commonly used units of kilo-ohm (KΩ), megohm (MΩ). 1 MΩ = 1000 KΩ
1 KΩ = 1000Ω
7, what is Ohm's law for partial circuits?
The current flowing through a circuit is directly proportional to the voltage across the circuit and inversely proportional to the resistance of the circuit, a relationship called Ohm's law. This relationship is called Ohm's law. It is expressed by the formula I=U/R
Where: I - current (A); U - voltage (V); R - resistance (Ω).
Ohm's law for partial circuits reflects the interrelationships of voltage, current, and resistance in partial circuits, and it is the main basis for analyzing and calculating partial circuits.
8. What is Ohm's law for full circuits? With an electric potential of the full circuit diagram:
In the figure r0 is the internal resistance of the power supply; when the resistance of the wire is negligible, the load resistance R is the resistance of the external circuit; E represents the electric potential of the power supply. S represents the switch; I represents the current; U represents the voltage at the ends of the power supply.
When the switch S is closed and on, there will be current in the circuit, according to the part of the circuit Ohm's law, in the external circuit of the load resistor R on the resistance drop is equal to I × R = U, and in the internal circuit of the power supply on the internal resistance of the power supply r0 drop in the voltage for the U0 = I × r0.
Therefore, the full circuit of Ohm's law of the mathematical expression is:
E = U + U0 = IR + I r0 where current I=E/(R+ r0) where:E - power supply potential (V); R - external circuit resistance (Ω); r0 - power supply internal resistance (Ω). Full circuit Ohm's law is defined as: in a closed circuit, the magnitude of the current is proportional to the electromotive force of the current, and inversely proportional to the sum of the internal and external resistance of the entire circuit.
In other words, IR = E-I r0, that is, U = E-I r0, which indicates that the voltage U across the power supply is going to decrease as the current increases. Because the greater the current, the greater the internal resistance voltage drop I r0, so the output voltage U at the ends of the power supply decreases. Power supplies have internal resistance, the greater the internal resistance, with the change in current, the greater the change in power supply output voltage. When the internal resistance of the power supply is very small (relative to the load resistance), the internal resistance voltage drop can be ignored, it can be considered that U = E - I r0 ≈ E, that is, the terminal voltage of the power supply is approximately equal to the power supply electromotive force. 9, what are the three elements of alternating current?
Maximum value, period (or frequency), and initial phase.
10. What is the significance of increasing power factor?
To increase the utilization of power supply equipment.
Improvement in transmission efficiency.
Improvement in voltage quality.
11, What is undercompensation? Overcompensation? Full compensation?
Uncompensated means that the current I is lagging behind the voltage U, and the circuit is operating under an inductive load. In this case, the circuit has a low power factor and needs to be compensated.
Overcompensation means that the current I is ahead of the voltage U and the circuit is operating under a capacitive load. At this point, the circuit voltage rises and compensation needs to be reduced or withdrawn.
Fully compensated means that the voltage U is in phase with the current I, and the circuit is operating under a resistive load. Due to the complexity of the load, it is not possible to achieve full compensation.
Second, the basics of electrical distribution
1, what is the power grid?
By the various voltage levels of transmission lines and various types of substations connected to the network called the power grid. 2, the classification of the power grid?
The power network according to its role in the power system, divided into transmission and distribution networks of two types.
Transmission network is a high voltage or even ultra-high voltage power plants, substations or substations between the first library network connected to the power delivery network, so it can also be called the power network. Main grid.
The distribution network is the network that delivers electricity directly to customers.
The voltage of the distribution network is divided into:
High-voltage distribution network (35KV and above);
Medium-voltage distribution network (10KV, 6KV, 3KV voltage);
Low-voltage distribution network (220V, 380V voltage).
3, the company's power network belongs to the type?
All of our power grids are distribution grids. They are divided into two types: medium-voltage distribution network (110KV/10KV at the main bucking station) and low-voltage distribution network (10KV/380V at the workshop bucking station).
4, the transformer regulator?
Transformer voltage regulation is divided into two types of non-excited voltage regulation and on-load voltage regulation.
Unexcited voltage regulation is in the transformer, the secondary side of the transformer are separated from the power supply, change the high-voltage side of the tap to change the number of turns of the winding for voltage regulation.
On-load voltage regulation is the use of on-load tap-changer, to ensure that the load current is not cut off in the case of high-voltage winding tap, to change the number of high-voltage turns for voltage regulation.
5, the company's transformer regulator?
The 110KV/10KV general step-down station adopts on-load voltage regulation;
The 10KV/380V workshop step-down station adopts non-excited voltage regulation.
6, the operating temperature of the transformer and the temperature rise range of those regulations?
The limit operating temperature of the transformer windings is 105 ℃ (maximum surrounding air temperature of 40 ℃); transformer oil temperature on the upper layer of the maximum temperature does not exceed 95 ℃; control of the upper layer of oil temperature should not exceed 85 ℃.
The working temperature rise of the transformer winding is 65℃ (when the surrounding air temperature is 40℃ at the highest);
The working temperature rise of the transformer upper oil temperature is 55℃ (when the surrounding air temperature is 40℃ at the highest).
7, the role of the transformer oil?
Excluding air, improve the insulation strength of the transformer, good heat dissipation so that the windings and the core is cooled to improve operating conditions.
8, transformer oil test items and test cycle?
Transformer oil test items are divided into: voltage test, dielectric loss test and simplified test.
Transformer oil test cycle:
35KV transformer at least once a year;
35KV transformer at least once every two years.
The number of test oil samples:
Withstand voltage test not less than 0.5L (about 0.45Kg);
Simplified test not less than 1L (about 0.9Kg).
9, the transformer oil fill the attention?
Transformers above 35KV should be replenished with the same grade of oil, and should be tested for voltage.
10KV and the following transformer can be replenished with different grades of oil, but should be mixed oil voltage test.
After replenishment of oil to check the gas relay, and timely release of gas. If after 24 hours, no problem, you can re-connect the heavy gas to the drop circuit.
10, What should I do during inspection?
1) Ensure a safe distance between the human body and the live conductor when inspecting high voltage equipment. Do not touch the insulated part of the equipment, prohibited to move or over the cover, and not to carry out other work.
2) When entering the high-voltage switch room, the door must be closed.
3) When inspecting the equipment, it should be carried out according to the specified equipment inspection route to prevent omission. Major equipment such as the main transformer should be around the tour for a week to check.
4) In the patrol inspection found problems, should be promptly reported to the leadership and recorded in the defects record.
5) In the equipment overload, heat, abnormal sound or bad weather, such as storms, snow, fog, freezing, nearby fire, etc. to carry out special inspections.
11. What is the scope of the work ticket?
The first kind of work ticket:
1) The work on the high-voltage equipment needs to be all or part of the blackout;
2) The work on the secondary wiring and lighting circuit in the high-voltage room, which needs to be blackout of the high-voltage equipment or to do the safety measures.
The second kind of work ticket:
1) charged work and work on the shell of the charged equipment;
2) the control panel of the low-voltage distribution panel, distribution box, power trunking work;
3) secondary wiring circuit work, without the need for high-voltage equipment de-energized;
4) the rotation of the generator, the same time the regulator camera. generator in rotation, the excitation circuit of the synchronous regulator or the work on the rotor resistance circuit of the high-voltage motor;
5) the measurement of the current in the high-voltage circuit by the off-duty duty personnel with the insulating rod and the voltage transformer to set the phase or with the clamp-on ammeter.
12, the requirements of verbal or telephone orders?
1) verbal or telephone orders, must be clear and correct, the duty officer should be issued by the person in charge and the task detailed in the operating record book, and to the issuer to recite the check once.
2) Strictly implement the industry standardized terminology, to avoid misinterpretation of the contents of the order.
3) Accident repair work can not use the work ticket, but should be recorded in the operation record book, before the start of the work must be in accordance with the provisions of the safety measures, and should be designated as a person responsible for monitoring.
Third, the basic knowledge of maintenance electrician
1, draw the process flow diagram of the firing system? (See the figure on the right.)
In the figure, a single solid line indicates the wind direction of the system;
Hollow line indicates the direction of material movement.
2. What are the main automated devices in the firing system?
The main automation devices in the firing system are temperature and pressure instruments.
3. Where are the main automation devices installed in the firing system?
1) C1 outlet temperature, pressure;
2) C2 outlet temperature, pressure;
3) C3 outlet temperature, pressure;
4) C4 outlet temperature, pressure;
5) C5 outlet temperature, pressure;
6) C4 cone pressure and downstream temperature
7) C5 Cone temperature and discharge temperature;
8) Decomposition furnace outlet temperature;
9) Decomposition furnace body temperature;
10) Kiln tail flue chamber temperature and pressure;
11) Kiln header temperature and pressure;
4. What is the specific role of automation equipment for process operations?
The automation equipment is the eyes of the process operation; it provides key operational data to the production operation; it is the key equipment to guarantee the yield and quality.
5. How many types of temperature sensors do you use?
There are two main types of temperature detecting components used in our company: K scale thermocouples and Pt100 scale platinum RTDs. However, the thermocouple specifications are different, due to the different working environment, to the castor cold machine shape encapsulation material is different, so the specific type of thermocouple in different installation locations, specifications and encapsulation materials are different. Platinum RTD specifications are also different, due to different working environments, the shape of the encapsulation material is different, so different installation locations of the RTD specific models, specifications and encapsulation materials are also different.
6, What is a DCS system?
DCS system is a distributed industrial control system composed mainly of computers.
7, DCS system has several main control methods?
There are two main control methods for DCS systems: switching control and analog control.
8, What are the basic concepts of sensors?
A variety of non-electrical signals into electrical signals, the device is called a sensor.
Non-electrical signals: temperature, pressure, displacement, vibration, light, weight, flow, gas, sound, color, etc. are non-electrical signals.
9, What are the basic concepts of switching and analog signals?
Switching signals: only two states, on or off. Most of the control of various electrical devices are controlled by switching signals.
Analog signals: A signal that changes continuously and linearly is called an analog signal. A variety of non-electrical signals converted into electrical signals, except in some cases, generally belong to the analog signal.
10, how is the sensitivity of load cell expressed? What does it mean?
The sensitivity of a load cell is expressed in mV/V.
This is the same as the sensitivity of a load cell.
This means that when the bridge excitation voltage input is 1V, it corresponds to the output voltage value at full scale. In general, the sensitivity of a load cell is between 1 and 3 mV/V.
11, how to judge the load cell?
Since the color of the load cell lead varies from manufacturer to manufacturer, you can't judge the function of the lead by its specific color.
The resistance of the multimeter can be used to determine the function of the lead and the sensor: (see figure)
Note: If there is unequal data, the sensor is damaged and should be replaced.
12, the normal current of the compensation capacitor is equal to how much?
1) Determine the capacitance (empirical formula):
Rated operating voltage 400V: 1KVAr×19.9=19.9μF
25KVAr×19.9=497.5μF 30 KVAr×19.9=597μF
Our low-voltage compensation capacitors are these Two kinds of capacitors.
2)Relationship between capacitance and current (empirical formula):
C=14×I (rated working voltage 400V)
C÷14=I
497.5÷14=35.5A≈36A (25KVAr)
597÷14=42.6A≈43A (30KVAr)
597÷14=42.6A≈43A (30KVAr)
597÷14=42.6A≈43A (25KVAr)
597÷14=42.6A≈43A (30KVAr). p>
3)Relationship between reactive power and current(empirical formula):
1 KVAr×1.44=1.44A (at rated working voltage 400V)
25 KVAr×1.44=36A
30 KVAr×1.44=43.2A≈43A
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