Special Ground Connection On Equipment And Metal Structures (part 1 - For Switchyards And Sub-stations)

SPECIAL GROUND CONNECTION ON EQUIPMENT AND METAL STRUCTURES (PART 1 - FOR SWITCHYARDS AND SUB-STATIONS)

 Objectives  Introduction  General Fundamentals  Effects of Electric Shock to Human Body

 Grounding and Bonding  Ground

and Bonding in Commercial and Industrial

Facilities  Special Grounding Connection in Facilities Over 1000 Volts

(Switchyard and Sub-station Equipment and Structures)

 To be able to have comprehensive understanding on

the concepts of Grounding and Bonding  To be able to understand the specific applications of

Grounding and Bonding  To be able to understand the special grounding

requirements of equipment and metal structures in switchyards and sub-stations To be able to apply the proper grounding methods for

switchyard and sub-station equipment and structures

What is GROUNDING SYSTEMS?

GROUNDING SYSTEM Defined by IEEE Std. 142-2007 (Green BooK) as:

system that consists of all interconnected grounding connections in a specific power system and is defined by its isolation from adjacent grounding systems. • The isolation is provided by transformer primary and secondary windings that are coupled only by magnetic means. •A

the system boundary is defined by the lack of a physical connection that is either metallic or through a significantly high impedance.

• Thus,

WHY INSTALL GROUNDING SYSTEMS?

Purpose of Grounding System •

Personnel Safety • Low impedance grounding and bonding between metallic equipment, chassis, piping and other conductive objects so that fault fault and lightning currents do not result to voltages that can cause a shock hazard •

Proper grounding facilitates operation of the overcurrent protective device during ground faults.

•

Equipment and Building Protection • Low impedance grounding and bonding between electrical services, protective devices, equipment and other conductive objects so that fault and lightning currents do not result in hazardous voltages inside the building. •

Proper operation of overcurrent protective devices is frequently depended upon low impedance current paths.

•

Electrical Noise Reduction • Proper grounding aids in electrical noise reduction •

Ensures that: 1.

The impedance between the signal ground points throughout the building is minimized.

2.

Voltage potentials between interconnected equipment are minimized.

3.

Effects of electrical and magnetic coupling are minimized.

General Types of Grounding •

Power System Grounding Including the Service Entrance

•

Bonding

•

Grounding Electrical Equipment

•

Lightning Protection

•

Protection of Electronic Equipment

ELECTRICAL CIRCUITRY BASICS

TRUE OR FALSE? A.

ELECTRIC CURRENT TAKES THE PATH OF LEAST RESISTANCE FALSE

B.

ELECTRIC CURRENT WILL TAKE ALL PATHS OR CIRCUITS THAT ARE AVAILABLE TRUE

OHMS LAW IN REVIEW

RESISTANCE VS. IMPEDANCE Resistance (R) •

The total opposition to current in a DC circuit.

Impedance (Z) • The total opposition to current an AC circuit. • Comprised of three components namely the Inductive Reactance (XL), Capacitive Reactance (XC), and the Resistance (R) added together vectorially • Frequency-dependent – changes in magnitude as frequency changes

Inductive Reactance (XL) = 2πFL • Where F = frequency (Hz); L = inductance (Henry) • Directly proportional to frequency – increases in magnitude while frequency increases

Capacitive Reactance (XC) = 1 / 2πFC • Where F = frequency (Hz); C = Capacitance (Farad) • Inversely proportional to frequency – decreases in magnitude while frequency increases

CURRENT IN A CIRCUIT •

In any complete circuit or path that is available, current—be it normal current or fault current—will always try to return to its source

•

Electrical current will take any and all available paths to return to its source.

CURRENT IN A CIRCUIT •

If several paths are available, current will divide and the resistance or the impedance of each path will determine the magnitude of current on that particular path.

•

Thus, if there is no complete circuit, then there is no current.

CURRENT IN A CIRCUIT If several paths are available, current will divide and the resistance or the impedance of each path will determine the magnitude of current on that particular path. • Thus, if there is no complete circuit, then there is no current.

EFFECTS OF ELECTRIC SHOCK TO THE HUMAN BODY

WHAT IS GROUNDING & BONDING?

GROUNDING Defined as:

to ground or to a conductive body that extends the ground

• Connecting

to a common point which is connected back to the electrical source. It may or may not be connected to earth (i.e. in aircrafts)

• Connecting

• Earthing

is a common term outside the US and is the connection between equipment and facilities, grounds to mother earth (necessary for lightning protection systems)

SYSTEM GROUNDING

Defined as: • the intentional connection to ground through a ground electrode conductor (GEC) of a phase or neutral conductor

•

Purpose of System Grounding •

Controlling the voltage with respect to earth, or ground, within predictable limits

•

Providing for a flow of current that will allow detection of an unwanted connection between system conductors and ground.

•

Such detection may then initiate operation of automatic devices to remove the source of voltage from these conductors.

TYPES OF SYSTEM NEUTRAL GROUNDING •

Ungrounded System or Capacitance Grounded System

•

Solidly-Grounded System

•

Impedance Grounded System 1. 2. 3.

Reactance Grounded System Resistance Grounded System Ground-Fault Neutralizer System

•

Ungrounded System Grounded System •

or

Capacitance

No intentional connection between the system conductors and ground.

•

Solidly-Grounded Systems •

the connection of a system conductor, usually the neutral of a generator, power transformer, or grounding transformer directly to ground, without any intentional intervening impedance.

BONDING Defined as: • Permanent

joining of metallic parts to form an electrically conductive path electrical continuity and capacity to conduct any current safely that is likely to be imposed

• Ensures

• Minimize

potential difference between conductive components

•

Equipment Grounding • includes also the Equipment Grounding Conductor •

refers to the interconnection (bonding) and grounding of the nonelectrical metallic elements of a system

•

Such detection may then initiate operation of automatic devices to remove the source of voltage from these conductors.

•

Equipment Grounding 1.

To reduce electric shock hazard to personnel.

2.

To provide adequate current-carrying capability, both in magnitude and duration, to accept the ground-fault current permitted by the overcurrent protection system without creating a fire or explosive hazard to building or contents.

3.

To provide a low-impedance return path for ground-fault current necessary for the timely operation of the overcurrent protection system.

OVERCURRENT DEVICE OPERATION •

Overcurrent devices operate because of more current (amps) flowing than the device is rated to carry

•

Overcurrent protection devices are designed to operate in inverse time thus the more current through overcurrent devices above their rating the faster they open or operate;

•

The higher the impedance of the path, the lower the current through the overcurrent device and therefore longer time to open.

•

The lower the impedance of the path, the greater is the current through the overcurrent device and faster opening time.

Grounding and Bonding for Commercial and Industrial Facilities

TYPICAL PLANT GROUNDING SYSTEM

TYPICAL PLANT GROUNDING ELECTRODE

TYPICAL BONDING METHODS

INSTRUMENTATION GROUNDING SYSTEM

Grounding and Bonding for Systems Over 1000 Volts

BASIC SHOCK SITUATIONS

Common Misconceptions about Grounding & Bonding

COMMON MISTAKES IN GROUNDING

AUXILIARY GROUNDING

ISOLATED GROUNDING