Ungrounded Systems in Electrical Engineering

Questions and Answers

What is the date of the maintenance on ground or replace?

February 8, 2001

January 7, 2001

January 9, 2001

January 8, 2001 (correct)

What is the temperature mentioned in the ambient conditions?

75 °F

85 °F

80 °F

83 °F (correct)

What is the name of the engineer mentioned in the report?

James Johnson

John Smith

Harry Tittel, E.E. (correct)

Michael Brown

What is the test method used in the earth ground test?

Clamp on Ground Tester Signup and view all the answers

What is the address of Florida Electrical Resources?

6550 New Tampa Hwy., Suite B Signup and view all the answers

What is the phone number of Florida Electrical Resources?

(800) 727-4337 Signup and view all the answers

What is the typical range of ground fault current in an electrical system?

100-600 Amps Signup and view all the answers

What is the primary purpose of a system ground in an electrical circuit?

To protect equipment from damage Signup and view all the answers

What is the characteristic of a high resistance grounded system?

Very low ground fault current Signup and view all the answers

What is the benefit of high resistance grounding in terms of transient overvoltages?

It limits transient overvoltages Signup and view all the answers

What is the primary application of high resistance grounding?

Situations where unplanned outages are unacceptable Signup and view all the answers

What is the purpose of a maintenance ground?

To ensure safe work practices Signup and view all the answers

What is unique about electronic and computer grounds?

They are combined with the system ground Signup and view all the answers

What is the benefit of system grounding in terms of motor insulation life?

It improves insulation life Signup and view all the answers

What is the typical resistivity of clay-sand-gravel mixtures?

145 ohm-cm Signup and view all the answers

Which type of soil has the highest resistivity?

Quartzite's, crystalline limestone, marble, crystalline rocks Signup and view all the answers

What is the characteristic of low resistivity soils?

They are highly influenced by the presence of moisture Signup and view all the answers

What is the typical resistivity of fine sandy or silty clays, silty clays, lean clays?

140 ohm-cm Signup and view all the answers

Which type of soil has a resistivity of 55 ohm-cm?

Silty or clayey fine sands with slight plasticity Signup and view all the answers

What is the characteristic of marls?

They are crumbly soil composed mostly of clay with a high limestone content Signup and view all the answers

What is the typical resistivity of gravel, gravel-sand mixtures?

800 ohm-cm Signup and view all the answers

What is the characteristic of decomposed granites, gneisses, etc.?

They have a resistivity of 300-500 ohm-cm Signup and view all the answers

What is the main characteristic of an ungrounded system?

It has a low ground fault current Signup and view all the answers

What happens to the neutral potential of an ungrounded system with balanced loading?

It becomes closer to ground potential Signup and view all the answers

What is a disadvantage of solidly grounded systems?

High magnitude fault currents Signup and view all the answers

What is the purpose of the grounding resistor in a low resistance grounded system?

To limit the ground fault current to a desired level Signup and view all the answers

What type of system is commonly used in low voltage distribution systems?

Solidly grounded system Signup and view all the answers

What happens to the voltage on unfaulted phases during a fault in a solidly grounded system?

It remains the same Signup and view all the answers

Why is low resistance grounding not recommended for low voltage systems?

Due to limited ground fault current Signup and view all the answers

What is an advantage of low resistance grounded systems?

Limits transient overvoltages during ground faults Signup and view all the answers

What is the amperage reading recorded at the Stacker, Sorter, C-N-S Area?

34 mA Signup and view all the answers

What is the resistance recorded in the test results?

1.5 Ω Signup and view all the answers

What is the temperature recorded in the ambient conditions?

93 °F Signup and view all the answers

What is the location of the test point?

Stacker, Sorter, C-N-S Area Signup and view all the answers

What is the company name mentioned at the bottom of the page?

Florida Electrical Resources Signup and view all the answers

What is the fax number of the company?

(863) 327-1091 Signup and view all the answers

What is the time of the test?

11:35 AM Signup and view all the answers

What is the ground condition mentioned in the ambient conditions?

Dry Ground Signup and view all the answers

Study Notes

Types of Grounding Systems

Ungrounded system: capacitively coupled, neutral potential close to ground potential due to capacitance between phase conductors and ground, low ground fault current, very high voltages on unfaulted phases, sustained faults lead to system line-to-line voltages on unfaulted lines, insulation failure, and failure due to restrike ground faults.

Solidly Grounded System

Neutral connected to ground without intentional impedance, large magnitude of current flow, aids in coordination, low initial cost, but stray currents may become a consequence, common in low voltage distribution systems, typically feeds to transformer primary with high side fuse protection, not preferred for industrial or commercial facilities due to high magnitude fault currents.

Low Resistance Grounded System

Neutral connected to ground through a small resistance, limits fault current, size of grounding resistor selected to detect and clear faulted circuit, limits transient overvoltages during ground faults, not recommended for low voltage systems due to limited ground fault current, ground fault current typically in the 100-600 Amp range.

High Resistance Grounded System

Neutral connected to ground through a resistive impedance, limits ground currents to a desired level, physically large resistor banks, very low ground fault current, typically under 10 Amps, special relaying methods utilized to detect and remove ground faults, typically applied to situations where it is essential to prevent unplanned outages, recent trend is to utilize high resistance grounding on 600 volt systems and lower.

Grounding Systems

System grounds: connected to earth, provides a low impedance path for fault currents, improves ground fault coordination, ensures longer insulation life of motors, transformers, and other system components.
Maintenance grounds: temporary ground, used for safe work practices.
Electronic and computer grounds: equipment ground and system ground combined and applied in unity.

Earth Ground Test Report

Earth ground test data: amperage reading, test results, notes, ground tested within parameters.
Test point digital image and location representation.
Test method: clamp on ground tester.
Client/facility: client name.
Engineer: Harry Tittel, E.E.
Date: January 8, 2001.
Ambient conditions: temperature, humidity, dry ground.
Test results: ohms reading, notes.

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Description

This quiz covers the characteristics of ungrounded systems in electrical engineering, including capacitively coupling, neutral potential, and fault currents. It also explores the effects of sustained faults and insulation failures.