July 21, 2023

Essential for weak current security personnel, popular, easy to understand, 0 foundation, easy to learn

Essential for weak current security personnel, popular, easy to understand, 0 foundation, easy to learn

There is nothing important but life and death, safety is an eternal theme. At present, China has become one of safest countries recognized internationally, which is inseparable from tacit dedication of security personnel.

From junior weak current security professional to senior or technical level, you need to keep learning and improving your technical level. Below are theoretical knowledge collected and sorted by Yianfang in hope of helping you.


Connection diagram

There is a principle when looking at electrical schematics and electrical schematics: top to bottom, left to right.

Study principle of connection in detail, remember thousands of information.

Title block, component list, reading description, drawing number

From general to local and then from power supply to load.

For main circuit see details, for subcircuit don't forget

There is an order from top to bottom, and no missing elements from left to right.

Energy path, information flow, tables and diagrams to be understood

Analyze signal line from power supply to load and secondary circuit.

List of materials, design documentation, general requirements, catalog number

Look at detailed description of drawing and key points of understanding drawing will become clear.

Look at principle, divided into main and auxiliary, AC and DC, subdivided and understood,

First look at each power supply circuit and protection, measurement and control will become clear.

Installation diagram, for main and auxiliary, through line, to load,

Don't forget power supply section, components are connected in series.

Expanded scheme, when reading, by principle, in a cycle,

The function keys of electrical components are drawn between lines respectively.

Plan view, sectional view, look at civil engineering, look at pipelines,

Electrical equipment has an arrangement, carefully look at dimensions and projections.

Connection lines, information transfer, logic display, connection functions

Despite bulkiness of multi-line view, it is intuitive, detailed, and easily distinguishable.

The one-line method is also simple. It shows three phases and should be symmetrical.

Mutual induction relay with one image, multi-line text for detailed description.

Shading, thick and thin lines, adding text, drawing slanted lines

Mark wire types and mark middle of wide and thick part.

Cross-shaped, even T-shaped, intersection of wires, connected or not,

Just look at little dot in center, it's easy to see.

Insulated wire to be marked, slave end, independent wire,

Combinedlabel function key, protection between polarity and phase.

Components, graphic numbers, simplified forms, element numbers

Focus on presenting simple charts and separate them for presenting advanced charts.

Working condition, drawing is normal, contact point, direction is stable,

The rule is open on left and close on right, don't forget to open from bottom and close closed!

Parameter value, data number marked in attachment

The comment sign must be clear, and there must be a small dot on terminal chart.


A simple wire load rating

Ten below five, hundreds above two, two, five, three, five, four, three realms. Seventy-nine five times and a half, temperature is reduced by 10%, and copper upgrade counts.

Note: load capacity of aluminum conductors with a cross section of less than 10 square millimeters is calculated as 5 A/mm2, load capacity of aluminum conductors with a cross section of more than 100 mm2 is calculated as 2 A/mm2, load capacity of aluminum conductors with a cross section of 25 mm2 is calculated as 4 A/mm2. current-carrying capacity of an aluminum conductor with a cross section of 35 sq. mm is calculated at 3A/mm2, current-carrying capacity of an aluminum conductor with a cross section of 70 sq. mm and 95 sq. mm is calculated at 2.5 A/mm2.

Copper Upgrade Calculation: For example, to calculate power of 120mm2 copper conductors, you can select 150mm2 aluminum conductors to find capacitance of aluminum conductors; depends on temperature, finally multiply by 0.8 or 0.9 (depending on geographic location). ).


Find rated current from voltage side

Knowing power of transformer, find rated current on voltage level side: divide power by voltage value, multiply quotient by six and divide by ten.

Note. Suitable for any voltage level.

Example: apparent current I=apparent power S/1.732*10kV=1000kVA/1.732*10kV=57.736A

Rating I=1000kVA/10kV*6/10=60A


Quickly calculate current fuse value

Knowing power of transformer, quickly calculate current value of primary and secondary protective fuse (commonly called a fuse):

For distribution transformer high voltage fuse link, compare power and voltage.

For a low-voltage distribution transformer fuse, multiply power by 9 and divide by 5.


Nominal current search

If you know power of a three-phase motor, find its rated current: divide power by number of kilovolts and multiply quotient by a factor of seven or six.

A three-phase two-hundred-two-motor electric motor with a power of 3.5 amperes is known.


It is known that a high-voltage engine has three thousandvolt four kilowatts and one ampere.


Explanation: The formula is applicable for calculating rated current of three-phase motors of any voltage level. When using formulas, unit of power is kW, unit of voltage is kV, and unit of current is A.


Connecting a single-phase socket

There are many types of single-phase sockets, usually divided into two and three holes.

Two holes are located side by side and divided into left and right sides, and three holes form figure of character.

The letters are marked next to wiring hole, L means fire, and N means zero.

Three of holes have an E, which means ground is in middle.

Back to outlet to set direction, wiring of each hole has rules.

Connect neutral wire on left to fire wire on right, and connect PE wire to center.


Smart use of electric pen

Skillful use of electric pen to determine grounding fault of phase wire of three-phase three-wire 380/220V power supply line:

Three-phase line of star connection method, electric pen touches two bright lines.

The rest is weak and phase wire is grounded.

If there is almost no light, there is a short to metal ground.

Explanation: The secondary side of a power transformer is usually connected in a Y shape. In a three-phase three-wire system where neutral point is not earthed, when three-phase wires are touched with an electric control knob, two of them are usually a little brighter, and other one If brightness of one line is weaker, this means that low brightness phase line has a grounding phenomenon, but it is not too serious; Ground error.


Engine wiring

2.5 add three, 4 add four, 6 add six, 25 five, 120 wires with hundreds.

Explanation: "25 five" means that starting from 25 square millimeters, term has changed from six to five. That is, 25 square millimeters can be equipped with 30 kilowatts, 35 square millimeters can be equipped with 40 kilowatts, 50 square millimeters can be equipped with 55 kilowatts, and 70 square millimeters can be equipped with 75 kilowatts.

"120 wires with hundreds" (read "120 wires with hundreds") means that engine power reaches 100 kilowatts. The cross section of wire does not match motor with magnification ratio, and wire of 120 square millimeters can only be matched with a 100 kW motor.


Relationship between impedance, reactance, inductive reactance and capacitive reactance

Inductive reactance is called inductive reactance and capacitive reactance is called ecapacitive reactance.

Inductance and capacitance are connected in series, inductive reactance, capacitance and reactance.

Resistance, inductance and capacitance are connected in series, and resistance, reactance and impedance are combined.

Each of three is on same side, and hooks, threads and ropes are arranged in series.

The Pythagorean theorem can be used and one side is known from both sides.



Fire wire L, neutral wire N, metal case ground E.

The neutral wire is grounded and there is electricity in fire, neon gas glow is a live wire, and neon tube is electricity. Stop a million.

Press tip of pen to connect wires, and be careful not to touch tip with your fingers.

In event of an electric shock, first turn off power and use an insulating rod to lift wire.

Live and neutral wires are laid side by side, and sockets are connected in parallel.

Earth on three-hole socket and fire to right of two-hole socket.

The light switch is connected to live wire, and neutral wire goes directly to lamp socket.

The fuse must be connected to fire wire and three-prong plug must be connected to housing.

What is done on paper is, after all, superficial, and I know that this work needs to be done. Yi Anfang suggested that after learning theoretical knowledge, you should do more practical operations to integrate theory into action.

Security is an important issue related to future and destiny of mankind. As China's first security and maintenance platform, Easy Security is willing to work with industry peers to help develop China's security industry!