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SEMI F49-0200 © SEMI 2000 7 factors i n determining the sag response of many common devi ces. 138kV (L-L Nom inal) φ C φ B φ A Subst ation T ransfo rmer First Ste p-down Transforme r Second Step-down Transformer 12.47 kV…

SEMI F49-0200 © SEMI 2000 6

7.6.3 Computer design tools should be used to model

the electrical distribution system in order to calculate

anticipated voltage sags for utility or site originated

faults. If limitations exist such that voltage sag

monitors are not located at every piece of equipment,

then event measurements can be adjusted from

modeling information to determine voltage sag values

at other locations.

7.6.4 As a means for measuring effectiveness in a

business environment, it would be useful to statistically

model the effect of voltage sag events on the

manufacturing processes. The variations mentioned in

Section 7.3.2, above, preclude a deterministic approach

to how well a wafer fabrication process will perform for

a given voltage sag event. A statistical correlation

model would aid in estimating the correlation between

voltage sags and manufacturing cost, and can be used to

validate the effectiveness of power enhancement and

conditioning programs.

7.6.5 Example of Voltage Sag Event Modeling

7.6.5.1 A voltage sag event originating on the

electrical utility system often exhibits different

characteristics when measured at different locations on

facility electrical distribution systems. The variance in

voltage sag characteristics can create different effects

on similar equipment. Variances can usually be

explained by examining 1) the characteristics of voltage

sag at the utility interfaces, 2) the type and connection

configuration of voltage transformations, and 3) the

voltage levels and corresponding phase relationships at

the terminals of infrastructure, support, and process

equipment within the facility.

7.6.5.2 The types of faults that can occur on a utility

system are:

• Line to line to line,

• Line to line to line to ground,

• Line to line,

• Line to line to ground, and

• Line to ground.

7.6.5.3 The utility network can be modeled to predict

the voltage sag characteristics due to various types of

faults at the electrical interfaces between a

semiconductor manufacturing facility and utility. The

most common utility system fault type is a single line to

ground fault. An example of the translation of a

voltage sag resulting from a line to ground voltage sag

event is provided in the following sections.

7.6.5.4 Typical voltage transformations from the

utility interface to utilization voltage levels are

illustrated in Figure 3. Under normal conditions, the

three phase voltages are all approximately equal and

displaced 120º from each other. During a voltage sag

event due to an unbalanced fault, this relationship

changes. Delta-wye transformers between the origin of

the fault and the equipment being studied will further

affect the phase and magnitude relationships. The

degree to which voltage phase shift and magnitude

changes occur at each transformation throughout the

facility distribution system should be considered when

examining impacts on individual equipment.

Transmission System

Medium Voltage Distribution System

138kV (L-L Nominal)

Substation Transformer

First Step-down Transformer

Second Step-down Transformer

Low Voltage Distribution System

12.47 kV (L-L Nominal) 7.2 kV (L-N Nominal)

480 or 208 volt (L-L) 277 or 120 volt (L-N)

208 volt (L-L) 120 volt (L-N)

Figure 3

Typical Semiconductor Factory Voltage

Transformations

7.6.5.5 Figure 4 illustrates the variations in magnitude

of a voltage sag event within a facility during a single

line to ground fault on a utility transmission line. This

example illustrates a worst case situation, where a

single-phase fault occurs at a substation transformer

primary-side terminal. (See Related Documents

section.)

7.6.5.6 Many devices in process, support, and facilities

infrastructure equipment are not connected to all three

phases. Because the voltage sag response of these

devices may dictate the sag response for the entire

equipment assembly, understanding device connection

configuration and sag response characteristics is of

critical importance. Sag depth and duration, the point

on the wave at which the sag begins, and the

corresponding phase relationships are all known to be

SEMI F49-0200 © SEMI 20007

factors in determining the sag response of many

common devices.

138kV (L-L Nominal)

Substation Transformer

First Step-down Transformer

Second Step-down Transformer

12.47 kV (L-L Nominal) 7.2 kV (L-N Nominal)

480 or 208 volt (L-L) 277 or 120 volt (L-N)

208 volt (L-L) 120 volt (L-N)

Sag Voltage

(% of Normal)

58%

100%

58%

Sag Voltage

(% of Normal)

88%

33%

Sag Voltage

(% of Normal)

58%

100%

58%

Sag Voltage

(% of Normal)

58%

100%

58%

Sag Voltage

(% of Normal)

88%

33%

Sag Voltage

(% of Normal)

88%

33%

Sag Voltage

(% of Normal)

58%

100%

58%

L-G Fault

Figure 4

Example of Voltage Sag Levels during a Single Line

to Ground Fault

7.6.5.7 Figure 4 illustrates the importance of phase

relationships in the sag response of a 120-volt control

circuit emergency off (EMO) relay which is connected

to phase A (or phase B) in a 208-volt facility

distribution system derived with only one low voltage

transformation. In this example the voltage sags to only

88% of nominal on these phases, but drops to 33% of

nominal on phase C. The industry specification for

semiconductor processing equipment voltage sag

immunity does not specify that equipment ride-through

a sag to 33% of nominal voltage.

7.6.5.8 If two low voltage transformations were used

to derive the 208-volt facility system (see Figure 4),

phase B voltage would be unaffected during the utility

voltage sag, but phases A and C would sag to 58% of

nominal. Industry standards typically require

equipment to ride-through a sag of this depth.

However, a tolerance designed into the facility system

may be necessary to provide adequate system

protection.

7.7 Power Enhancing and Conditioning Strategies

7.7.1 While it is desirable to reduce and eliminate

battery storage devices provided by equipment

suppliers with individual pieces of process equipment,

battery storage devices may be appropriate as a

centralized or distributed part of a facilities distribution

system (when evaluated in a systems approach to power

enhancement and conditioning).

7.7.2 Facility power systems enhancements should be

examined on a case-by-case approach to determine the

appropriate measure of power conditioning to be

applied. In general, the following types of equipment

are frequently used to mitigate the effects of utility

voltage sag events in semiconductor factories.

• Constant voltage transformers (typically applied on

control systems)

• Diesel engine based uninterruptible power supplies

(UPS)

• Magnetic synthesizers

• Motor-generators

• Rotary UPS

• Static UPS

• Static transfer switches with alternate power

systems

7.7.3 Other power enhancement techniques and

equipment available for use in facilities electrical

distribution systems include but are not limited to the

following:

• Capacitors for voltage regulation,

• Filters for power conditioning,

• High resistance grounding,

• Isolation of electrical circuit from other loads,

• Power line conditioners,

• Primary and secondary selective rather than radial

distribution systems,

• Super-conducting magnetic energy storage

systems,

• Transformer load tap changers, and

• Voltage regulators.

7.7.4 Power enhancement and conditioning equipment

can be applied at selected equipment components,

selected distribution circuits, or selected distribution

buses. For power conditioning equipment application

guidelines see IEEE 1100 and 1346.

8 Related Documents

8.1 SEMI Standards

Under development.

8.2 CENELEC Standard

EN 50082-2 — Electromagnetic compatibility -

Generic immunity standard, Part 2. Industrial

environments.

8.3 IEC Standard

IEC 61000-4-11 — Electromagnetic Compatibility

(EMC) - Part 4: Testing and Measuring Techniques -

Section 11: Voltage Dips, Short Interruptions and

Voltage Variations Immunity Tests

8.4 IEEE Standards

IEEE Std 493 — IEEE Recommended Practice for the

Design of Reliable Industrial and Commercial Power

Systems

IEEE Std 1250 — IEEE Guide for Service to

Equipment Sensitive to Momentary Voltage

Disturbances

NOTE 2: As listed or revised, all documents cited shall be the

latest publications of adopted standards.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the guides set

forth herein for any particular application. The

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change without notice.

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2 European Committee for Electrotechnical Standardization

(CENELC), Rue de Stassart, 35, B - 1050 Brussels

3 International Electrotechnical Commission (IEC), 3 rue de

Varembé, PO Box 131, 1211 Geneva 20, Switzerland

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o

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