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In the network, whenever a fault occurs it results in the flow of large chunks of current across more than one phase and the ultimate result is what we call as short circuit.Here All You Need To Know About Short Circuits .

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How to Protect Household Appliances From Electrical Disaster. Here, look at the Electrical protection devices that you can install to protect your home from any of the aforementioned disasters .

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See the Latest Trends In Lighting Your Dream Home In 2018

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Switch Gear Protection Devices | Anchor

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Basic Motor Formulas And Calculations

The formulas and calculations which appear below should be used for estimating purposes only. It is the responsibility of the customer to specify the required motor Hp, Torque, and accelerating time for his application. The salesman may wish to check the customers specified values with the formulas in this section, however, if there is serious doubt concerning the customers application or if the customer requires guaranteed motor/application performance, the Product Department Customer Service group should be contacted.

Rules Of Thumb (Approximation)

At 1800 rpm, a motor develops a 3 lb.ft. per hp

At 1200 rpm, a motor develops a 4.5 lb.ft. per hp

At 575 volts, a 3-phase motor draws 1 amp per hp

At 460 volts, a 3-phase motor draws 1.25 amp per hp

At 230 volts a 3-phase motor draws 2.5 amp per hp

At 230 volts, a single-phase motor draws 5 amp per hp

At 115 volts, a single-phase motor draws 10 amp per hp

Mechanical Formulas

Torque in lb.ft. = HP x 5250

rpm HP = Torque x rpm

5250 rpm = 120 x Frequency

No. of Poles

Temperature Conversion

Deg C = (Deg F - 32) x 5/9

Deg F = (Deg C x 9/5) + 32

High Inertia Loads

t = WK2 x rpm

308 x T av. WK2 = inertia in lb.ft.2

t = accelerating time in sec.

T = Av. accelerating torque lb.ft..

T = WK2 x rpm

308 x t

inertia reflected to motor = Load Inertia Load rpm

Motor rpm 2

Synchronous Speed, Frequency And Number Of Poles Of AC Motors

ns = 120 x f

P f = P x ns

120 P = 120 x f

ns

Relation Between Horsepower, Torque, And Speed

HP = T x n

5250 T = 5250 HP

n n = 5250 HP

T

Motor Slip

% Slip = ns - n

ns x 100

Symbols

I = current in amperes

E = voltage in volts

KW = power in kilowatts

KVA = apparent power in kilo-volt-amperes

HP = output power in horsepower

n = motor speed in revolutions per minute (RPM)

ns = synchronous speed in revolutions per minute (RPM)

P = number of poles

f = frequency in cycles per second (CPS)

T = torque in pound-feet

EFF = efficiency as a decimal

PF = power factor as a decimal

Basic Horsepower Calculations

Horsepower is work done per unit of time. One HP equals 33,000 ft-lb of work per minute. When work is done by a source of torque (T) to produce (M) rotations about an axis, the work done is:

radius x 2 x rpm x lb. or 2 TM

When rotation is at the rate N rpm, the HP delivered is:

HP = radius x 2 x rpm x lb.

33,000 = TN

5,250

For vertical or hoisting motion:

HP = W x S

33,000 x E

Where:

W = total weight in lbs. to be raised by motor

S = hoisting speed in feet per minute

E = overall mechanical efficiency of hoist and gearing. For purposes of estimating

E = .65 for eff. of hoist and connected gear.

For fans and blowers:

HP = Volume (cfm) x Head (inches of water)

6356 x Mechanical Efficiency of Fan

Or

HP = Volume (cfm) x Pressure (lb. Per sq. ft.)

3300 x Mechanical Efficiency of Fan

Or

HP = Volume (cfm) x Pressure (lb. Per sq. in.)

229 x Mechanical Efficiency of Fan

For purpose of estimating, the eff. of a fan or blower may be assumed to be 0.65.

Note: Air Capacity (cfm) varies directly with fan speed. Developed Pressure varies with square of fan speed. Hp varies with cube of fan speed.

For pumps:

HP = GPM x Pressure in lb. Per sq. in. x Specific Grav.

1713 x Mechanical Efficiency of Pump

Or

HP = GPM x Total Dynamic Head in Feet x S.G.

3960 x Mechanical Efficiency of Pump

where Total Dynamic Head = Static Head + Friction Head

For estimating, pump efficiency may be assumed at 0.70.

Accelerating Torque

The equivalent inertia of an adjustable speed drive indicates the energy required to keep the system running. However, starting or accelerating the system requires extra energy.

The torque required to accelerate a body is equal to the WK2 of the body, times the change in RPM, divided by 308 times the interval (in seconds) in which this acceleration takes place:

ACCELERATING TORQUE = WK2N (in lb.ft.)

308t

Where:

N = Change in RPM

W = Weight in Lbs.

K = Radius of gyration

t = Time of acceleration (secs.)

WK2 = Equivalent Inertia

308 = Constant of proportionality

Or

TAcc = WK2N

308t

The constant (308) is derived by transferring linear motion to angular motion, and considering acceleration due to gravity. If, for example, we have simply a prime mover and a load with no speed adjustment

The formulas and calculations which appear below should be used for estimating purposes only. It is the responsibility of the customer to specify the required motor Hp, Torque, and accelerating time for his application. The salesman may wish to check the customers specified values with the formulas in this section, however, if there is serious doubt concerning the customers application or if the customer requires guaranteed motor/application performance, the Product Department Customer Service group should be contacted.

Rules Of Thumb (Approximation)

At 1800 rpm, a motor develops a 3 lb.ft. per hp

At 1200 rpm, a motor develops a 4.5 lb.ft. per hp

At 575 volts, a 3-phase motor draws 1 amp per hp

At 460 volts, a 3-phase motor draws 1.25 amp per hp

At 230 volts a 3-phase motor draws 2.5 amp per hp

At 230 volts, a single-phase motor draws 5 amp per hp

At 115 volts, a single-phase motor draws 10 amp per hp

Mechanical Formulas

Torque in lb.ft. = HP x 5250

rpm HP = Torque x rpm

5250 rpm = 120 x Frequency

No. of Poles

Temperature Conversion

Deg C = (Deg F - 32) x 5/9

Deg F = (Deg C x 9/5) + 32

High Inertia Loads

t = WK2 x rpm

308 x T av. WK2 = inertia in lb.ft.2

t = accelerating time in sec.

T = Av. accelerating torque lb.ft..

T = WK2 x rpm

308 x t

inertia reflected to motor = Load Inertia Load rpm

Motor rpm 2

Synchronous Speed, Frequency And Number Of Poles Of AC Motors

ns = 120 x f

P f = P x ns

120 P = 120 x f

ns

Relation Between Horsepower, Torque, And Speed

HP = T x n

5250 T = 5250 HP

n n = 5250 HP

T

Motor Slip

% Slip = ns - n

ns x 100

Symbols

I = current in amperes

E = voltage in volts

KW = power in kilowatts

KVA = apparent power in kilo-volt-amperes

HP = output power in horsepower

n = motor speed in revolutions per minute (RPM)

ns = synchronous speed in revolutions per minute (RPM)

P = number of poles

f = frequency in cycles per second (CPS)

T = torque in pound-feet

EFF = efficiency as a decimal

PF = power factor as a decimal

Basic Horsepower Calculations

Horsepower is work done per unit of time. One HP equals 33,000 ft-lb of work per minute. When work is done by a source of torque (T) to produce (M) rotations about an axis, the work done is:

radius x 2 x rpm x lb. or 2 TM

When rotation is at the rate N rpm, the HP delivered is:

HP = radius x 2 x rpm x lb.

33,000 = TN

5,250

For vertical or hoisting motion:

HP = W x S

33,000 x E

Where:

W = total weight in lbs. to be raised by motor

S = hoisting speed in feet per minute

E = overall mechanical efficiency of hoist and gearing. For purposes of estimating

E = .65 for eff. of hoist and connected gear.

For fans and blowers:

HP = Volume (cfm) x Head (inches of water)

6356 x Mechanical Efficiency of Fan

Or

HP = Volume (cfm) x Pressure (lb. Per sq. ft.)

3300 x Mechanical Efficiency of Fan

Or

HP = Volume (cfm) x Pressure (lb. Per sq. in.)

229 x Mechanical Efficiency of Fan

For purpose of estimating, the eff. of a fan or blower may be assumed to be 0.65.

Note: Air Capacity (cfm) varies directly with fan speed. Developed Pressure varies with square of fan speed. Hp varies with cube of fan speed.

For pumps:

HP = GPM x Pressure in lb. Per sq. in. x Specific Grav.

1713 x Mechanical Efficiency of Pump

Or

HP = GPM x Total Dynamic Head in Feet x S.G.

3960 x Mechanical Efficiency of Pump

where Total Dynamic Head = Static Head + Friction Head

For estimating, pump efficiency may be assumed at 0.70.

Accelerating Torque

The equivalent inertia of an adjustable speed drive indicates the energy required to keep the system running. However, starting or accelerating the system requires extra energy.

The torque required to accelerate a body is equal to the WK2 of the body, times the change in RPM, divided by 308 times the interval (in seconds) in which this acceleration takes place:

ACCELERATING TORQUE = WK2N (in lb.ft.)

308t

Where:

N = Change in RPM

W = Weight in Lbs.

K = Radius of gyration

t = Time of acceleration (secs.)

WK2 = Equivalent Inertia

308 = Constant of proportionality

Or

TAcc = WK2N

308t

The constant (308) is derived by transferring linear motion to angular motion, and considering acceleration due to gravity. If, for example, we have simply a prime mover and a load with no speed adjustment

HARMONICS Effects Basics:

1. The main problems caused by harmonic currents are:

a. Over-loading of neutrals

b. Increase of losses in the transformers

c. Increase of skin effect

2. The main effects of the harmonics voltages are:

d. Voltage distortion

e. Disturbances in the torque of induction motors

a. Overloading of neutrals

In a three phase symmetric and balanced system with neutral, the wave-forms Between the phases are shifted by a 120° phase angle so that, when the phases Are equally loaded, the current in the neutral is zero. The presence of unbalanced Loads (phase-to-phase, phase-to-neutral etc.) allows the flowing of an Unbalanced current in the neutral.

b. Increase of losses in the transformers

The effects of harmonics inside the transformers involve mainly three aspects:

i. The iron losses are due to the hysteresis phenomenon and to the losses Caused by eddy currents; the losses due to hysteresis are proportional to The frequency, whereas the losses due to eddy currents depend on the square Of the frequency.

ii. The copper losses correspond to the power dissipated by Joule effect in the Transformer winding. As the frequency rises (starting from 350 Hz) the current tends to thicken on the surface of the conductors (skin effect); under these circumstances, the conductors offer a smaller cross section to the current flow, since the losses by Joule effect increase. These two first aspects affect the overheating which sometimes causes a de-rating of the transformer.

iii. The third aspect is relevant to the effects of the triple-N harmonics (homopolar harmonics) on the transformer winding. In case of delta winding, the harmonics flow through the winding and do not propagate upstream towards the network since they are all in phase; the delta winding therefore represent a barrier for triple-N harmonics, but it is necessary to pay particular attention to this type of harmonic components for a correct dimensioning of the transformer.

c) Increase of skin effect

When the frequency rises, the current tends to flow on the outer surface of a Conductor. This phenomenon is known as skin effect and is more pronounced At high frequencies. At 50 Hz power supply frequency, skin effect is negligible, But above 350 Hz, which corresponds to the 7th harmonic, the cross section For the current flow reduces, thus increasing the resistance and causing Additional losses and heating. In the presence of high-order harmonics, it is necessary to take skin effect into Account, because it affects the life of cables. In order to overcome this problem, It is possible to use multiple conductor cables or bus bar systems formed by More elementary isolated conductors.

d) Voltage distortion

The distorted load current drawn by the nonlinear load causes a distorted voltage Drop in the cable impedance. The resultant distorted voltage waveform is applied To all other loads connected to the same circuit, causing harmonic currents to Flow in them, even if they are linear loads. The solution consists in separating the circuits which supply harmonic generating Loads from those supplying loads sensitive to harmonics.

e) Disturbances in the torque of induction motors

Harmonic voltage distortion causes increased eddy current losses in the motors, In the same way as seen for transformers. The additional losses are due to the generation of harmonic fields in the stator, each of which is trying to rotate the motor at a different speed, both forwards (1st, 4th, 7th, ...) as well as backwards (2nd, 5th, 8th, ...). High frequency currents induced in the rotor further increase losses.

1. The main problems caused by harmonic currents are:

a. Over-loading of neutrals

b. Increase of losses in the transformers

c. Increase of skin effect

2. The main effects of the harmonics voltages are:

d. Voltage distortion

e. Disturbances in the torque of induction motors

a. Overloading of neutrals

In a three phase symmetric and balanced system with neutral, the wave-forms Between the phases are shifted by a 120° phase angle so that, when the phases Are equally loaded, the current in the neutral is zero. The presence of unbalanced Loads (phase-to-phase, phase-to-neutral etc.) allows the flowing of an Unbalanced current in the neutral.

b. Increase of losses in the transformers

The effects of harmonics inside the transformers involve mainly three aspects:

i. The iron losses are due to the hysteresis phenomenon and to the losses Caused by eddy currents; the losses due to hysteresis are proportional to The frequency, whereas the losses due to eddy currents depend on the square Of the frequency.

ii. The copper losses correspond to the power dissipated by Joule effect in the Transformer winding. As the frequency rises (starting from 350 Hz) the current tends to thicken on the surface of the conductors (skin effect); under these circumstances, the conductors offer a smaller cross section to the current flow, since the losses by Joule effect increase. These two first aspects affect the overheating which sometimes causes a de-rating of the transformer.

iii. The third aspect is relevant to the effects of the triple-N harmonics (homopolar harmonics) on the transformer winding. In case of delta winding, the harmonics flow through the winding and do not propagate upstream towards the network since they are all in phase; the delta winding therefore represent a barrier for triple-N harmonics, but it is necessary to pay particular attention to this type of harmonic components for a correct dimensioning of the transformer.

c) Increase of skin effect

When the frequency rises, the current tends to flow on the outer surface of a Conductor. This phenomenon is known as skin effect and is more pronounced At high frequencies. At 50 Hz power supply frequency, skin effect is negligible, But above 350 Hz, which corresponds to the 7th harmonic, the cross section For the current flow reduces, thus increasing the resistance and causing Additional losses and heating. In the presence of high-order harmonics, it is necessary to take skin effect into Account, because it affects the life of cables. In order to overcome this problem, It is possible to use multiple conductor cables or bus bar systems formed by More elementary isolated conductors.

d) Voltage distortion

The distorted load current drawn by the nonlinear load causes a distorted voltage Drop in the cable impedance. The resultant distorted voltage waveform is applied To all other loads connected to the same circuit, causing harmonic currents to Flow in them, even if they are linear loads. The solution consists in separating the circuits which supply harmonic generating Loads from those supplying loads sensitive to harmonics.

e) Disturbances in the torque of induction motors

Harmonic voltage distortion causes increased eddy current losses in the motors, In the same way as seen for transformers. The additional losses are due to the generation of harmonic fields in the stator, each of which is trying to rotate the motor at a different speed, both forwards (1st, 4th, 7th, ...) as well as backwards (2nd, 5th, 8th, ...). High frequency currents induced in the rotor further increase losses.

RFI -Radio Frequency Interference Reduction in Drive:

In the use of Variable Frequency Drives or Adjustable Speed Drives, several types of emission may be generated on the power line. These might include low-order harmonics, or EMI/RFI noise. To provide a complete power line noise solution, frequencies from the 60Hz power line and above must be considered. This includes EMI/RFI noise in the 150kHz to 30MHz band which may interfere with TV’s, radios, computers, meters and controllers.

EMI/RFI Noise Reduction

Variable Frequency Drives (VFD’s) produce noise in the 150kHz to 30MHz band, primarily contained in the switching edges of the PWM controller. To reduce noise in that band, a filter containing a combination of high frequency inductors and capacitors may be utilized. To put it simply, inductors act as open circuits and the capacitors act as short circuits at high frequencies while passing the lower power line frequencies untouched. Thus the noise must pass through a nearly open circuit and what little gets through is then shorted out. Together, these parts can decrease noise to less that one one-thousandth (-60dB) of its original value in the critical band. The following graphic demonstrates basic operation.

Design Challenges

Reducing EMI/RFI (Electromagnetic/Radio-frequency Interference) noise using filtering technologies presents significant design challenges. Since high frequency energy can "jump" around components and travel along leads, filter designers must use high permeability ferrites, specialty capacitors, short, large diameter leads and small enclosures. As VFD’s produce noise primarily on the line with respect to ground, designers should focus on what is called "Common Mode" insertion loss. A 60dB-noise reduction from 150kHz to 30MHz should provide enough EMI/RFI noise reduction in the noted frequency band to limit the disturbance of other equipment on the power line.

Compliance to Noise Standards

Considering equipment disturbances that EMI conducted emissions can cause, industrial power line noise standards have been established worldwide. Among these are the American FCC15 subpart J class A, German VDE0871A and European CISPR11A and B (CE-EMI Directive) specifications.

Although each specification limits noise in a range, an overview shows that the main focus is on frequencies from 150kHz to 30MHz with a noise maximum of around 66dBm V (2mV) on the power line. A filter would need to bring noise signals down in the order of 2V down to the critical 2mV level.

To do this, a 1000:1 (60dB) reduction ratio is needed. This can be illustrated in a highly simplified model. If a 600V source is providing 16A, it has an effective impedance of 600/16=38 ohm . If the noise on the power line is 2V, then the noise current can be represented as 2/38=0.05A. The noise current to total current ratio is 0.05/16=0.33%. An effective filter would have a minimum insertion loss of 60dB into an ideal 50ohm resistor to match the reduction ratio needed and would be designed to accommodate a noise current ratio of 2-3%. This could theoretically provide 60dB reduction for up to a 15V line noise which could result in as large as a 15A noise current for a similarly designed 600A filter. One should choose filters with generous design margins to help reduce even the most difficult noise to meet world noise standards.

Correct Filter Application

An EMI/RFI filter will be most effective when installed correctly. Although the filter reduces noise on the power lines (conducted emissions), it should be located as close as practical to the drive to reduce broadcasting of the noise (radiated emissions) from the power lines themselves. As noise is shorted to ground through the capacitors, that short must be maintained by good grounding of the filter. A short, heavy, stranded conductor from the filter chassis to the drive’s main ground bus can achieve this.

A battery braid, Litz wire, or flexible welding cable with many fine strands is recommended for best grounding performance. Radiation of noise is also a concern for power line routing as it can effectively bypass the filter. Input and output filter leads should be separated by a maximum practical distance within enclosures and should be routed separately in interconnecting conduits when used.

A combination of good grounding and input/output lead separation will assure the best possible filter operation.

Part of the Complete Solution

As transistors in drives switch at higher frequencies, drives will come down in size and price. However, EMI/RFI emissions and the filtering technologies to address them are an important concern in good drive installations. EMI/RFI filters will become a part of the complete drive system. They will reduce power line emissions and interference associated with drives by reducing noise to limits that will not disturb nearby equipment and allow for compliance with agency guidelines.

In the use of Variable Frequency Drives or Adjustable Speed Drives, several types of emission may be generated on the power line. These might include low-order harmonics, or EMI/RFI noise. To provide a complete power line noise solution, frequencies from the 60Hz power line and above must be considered. This includes EMI/RFI noise in the 150kHz to 30MHz band which may interfere with TV’s, radios, computers, meters and controllers.

EMI/RFI Noise Reduction

Variable Frequency Drives (VFD’s) produce noise in the 150kHz to 30MHz band, primarily contained in the switching edges of the PWM controller. To reduce noise in that band, a filter containing a combination of high frequency inductors and capacitors may be utilized. To put it simply, inductors act as open circuits and the capacitors act as short circuits at high frequencies while passing the lower power line frequencies untouched. Thus the noise must pass through a nearly open circuit and what little gets through is then shorted out. Together, these parts can decrease noise to less that one one-thousandth (-60dB) of its original value in the critical band. The following graphic demonstrates basic operation.

Design Challenges

Reducing EMI/RFI (Electromagnetic/Radio-frequency Interference) noise using filtering technologies presents significant design challenges. Since high frequency energy can "jump" around components and travel along leads, filter designers must use high permeability ferrites, specialty capacitors, short, large diameter leads and small enclosures. As VFD’s produce noise primarily on the line with respect to ground, designers should focus on what is called "Common Mode" insertion loss. A 60dB-noise reduction from 150kHz to 30MHz should provide enough EMI/RFI noise reduction in the noted frequency band to limit the disturbance of other equipment on the power line.

Compliance to Noise Standards

Considering equipment disturbances that EMI conducted emissions can cause, industrial power line noise standards have been established worldwide. Among these are the American FCC15 subpart J class A, German VDE0871A and European CISPR11A and B (CE-EMI Directive) specifications.

Although each specification limits noise in a range, an overview shows that the main focus is on frequencies from 150kHz to 30MHz with a noise maximum of around 66dBm V (2mV) on the power line. A filter would need to bring noise signals down in the order of 2V down to the critical 2mV level.

To do this, a 1000:1 (60dB) reduction ratio is needed. This can be illustrated in a highly simplified model. If a 600V source is providing 16A, it has an effective impedance of 600/16=38 ohm . If the noise on the power line is 2V, then the noise current can be represented as 2/38=0.05A. The noise current to total current ratio is 0.05/16=0.33%. An effective filter would have a minimum insertion loss of 60dB into an ideal 50ohm resistor to match the reduction ratio needed and would be designed to accommodate a noise current ratio of 2-3%. This could theoretically provide 60dB reduction for up to a 15V line noise which could result in as large as a 15A noise current for a similarly designed 600A filter. One should choose filters with generous design margins to help reduce even the most difficult noise to meet world noise standards.

Correct Filter Application

An EMI/RFI filter will be most effective when installed correctly. Although the filter reduces noise on the power lines (conducted emissions), it should be located as close as practical to the drive to reduce broadcasting of the noise (radiated emissions) from the power lines themselves. As noise is shorted to ground through the capacitors, that short must be maintained by good grounding of the filter. A short, heavy, stranded conductor from the filter chassis to the drive’s main ground bus can achieve this.

A battery braid, Litz wire, or flexible welding cable with many fine strands is recommended for best grounding performance. Radiation of noise is also a concern for power line routing as it can effectively bypass the filter. Input and output filter leads should be separated by a maximum practical distance within enclosures and should be routed separately in interconnecting conduits when used.

A combination of good grounding and input/output lead separation will assure the best possible filter operation.

Part of the Complete Solution

As transistors in drives switch at higher frequencies, drives will come down in size and price. However, EMI/RFI emissions and the filtering technologies to address them are an important concern in good drive installations. EMI/RFI filters will become a part of the complete drive system. They will reduce power line emissions and interference associated with drives by reducing noise to limits that will not disturb nearby equipment and allow for compliance with agency guidelines.

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