Three Phase Transformers

Three Phase Transformer Basics

Thus far we have looked at the construction and operation of the single-phase, two winding voltage transformer which can be used

increase or decrease its secondary voltage with respect to the primary supply voltage. But voltage transformers can also be constructed

for connection to not only one single phase, but for two-phases, three-phases, six-phases and even elaborate combinations up to 24-phases

for some DC rectification transformers.

If we take three single-phase transformers and connect their primary windings to each other and their secondary windings to each other in a fixed configuration, we can use the transformers on a three-phase supply.

Three-phase, also written as 3-phase or 3φ supplies are used for electrical power generation, transmission, and distribution, as well as for all industrial uses. Three-phase supplies have many electrical advantages over Single-phase Power and when considering three-phase transformers we have to deal with three alternating voltages and currents differing in phase-time by 120 degrees as shown below.

Three Phase Voltages and Currents

Where: VL is the line-to-line voltage, and VP is the phase-to-neutral voltage.

A transformer can not act as a phase changing device and change single-phase into three-phase or three-phase into single phase. To make the transformer connections compatible with three-phase supplies we need to connect them together in a particular way to form a Three Phase Transformer Configuration.

A three phase transformer or 3φ transformer can be constructed either by connecting together three single-phase transformers, thereby forming a so-called three phase transformer bank, or by using one pre-assembled and balanced three phase transformer which consists of three pairs of single phase windings mounted onto one single laminated core.

The advantages of building a single three phase transformer is that for the same kVA rating it will be smaller, cheaper and lighter than three individual single phase transformers connected together because the copper and iron core are used more effectively. The methods of connecting the primary and secondary windings are the same, whether using just one Three Phase Transformer or three separate Single Phase Transformers. Consider the circuit below:

Three Phase Transformer Connections

The primary and secondary windings of a transformer can be connected in different configuration as shown to meet practically any requirement. In the case of three phase transformer windings, three forms of connection are possible: “star” (wye), “delta” (mesh) and “interconnected-star” (zig-zag).

The combinations of the three windings may be with the primary delta-connected and the secondary star-connected, or star-delta, star-star or delta-delta, depending on the transformers use. When transformers are used to provide three or more phases they are generally referred to as a Polyphase Transformer.

Three Phase Transformer Star and Delta Configurations But what do we mean by “star” (also known as Wye) and “delta” (also known as Mesh) when dealing with three-phase transformer connections. A three phase transformer has three sets of primary and secondary windings. Depending upon how these sets of windings are interconnected, determines whether the connection is a star or delta configuration.

The three available voltages, which themselves are each displaced from the other by 120 electrical degrees, not only decided on the type of the electrical connections used on both the primary and secondary sides, but determine the flow of the transformers currents.

With three single-phase transformers connected together, the magnetic flux’s in the three transformers differ in phase by 120 time-degrees. With a single the three-phase transformer there are three magnetic flux’s in the core differing in time-phase by 120 degrees.

The standard method for marking three phase transformer windings is to label the three primary windings with capital (upper case) letters A, B and C, used to represent the three individual phases of RED, YELLOW and BLUE. The secondary windings are labelled with small (lower case) letters a, b and c. Each winding has two ends normally labelled 1 and 2 so that, for example, the second winding of the primary has ends which will be labelled B1 and B2, while the third winding of the secondary will be labelled c1 and c2 as shown.

Transformer Star and Delta Configurations

Symbols are generally used on a three phase transformer to indicate the type or types of connections used with upper case Y for star connected, D for delta connected and Z for interconnected star primary windings, with lower case y, d and z for their respective secondaries. Then, Star-Star would be labelled Yy, Delta-Delta would be labelled Dd and interconnected star to interconnected star would be Zz for the same types of connected transformers.

Transformer Winding Identification

Connection Primary Winding Secondary Winding

Delta D d

Star Y y

Interconnected Z z

We now know that there are four ways in which three single-phase transformers may be connected together between primary and secondary three-phase circuits. The configurations are delta-delta, star-star, star-delta, and delta-star. Transformers for high voltage operation with the star connections has the advantage of reducing the voltage on an individual transformer, reducing the number of turns required and an increase in the size of the conductors, making the coil windings easier and cheaper to insulate than delta transformers.

The delta-delta connection nevertheless has one big advantage over the star-delta configuration, in that if one transformer of a group of three should become faulty or disabled, the two remaining ones will continue to deliver three-phase power with a capacity equal to approximately two thirds of the original output from the transformer unit.

Transformer Delta and Delta Connections

In a delta connected ( Dd ) group of transformers, the line voltage, VL is equal to the supply voltage, VL = VS. But the current in each phase winding is given as: 1/√3 × IL of the line current, where IL is the line current.

One disadvantage of delta connected three phase transformers is that each transformer must be wound for the full-line voltage, (in our example above 100V) and for 57.7 per cent, line current. The greater number of turns in the winding, together with the insulation between turns, necessitate a larger and more expensive coil than the star connection. Another disadvantage with delta connected three phase transformers is that there is no “neutral” or common connection.

In the star-star arrangement ( Yy ), (wye-wye), each transformer has one terminal connected to a common junction, or neutral point with the three remaining ends of the primary windings connected to the three-phase mains supply. The number of turns in a transformer winding for star connection is 57.7 per cent, of that required for delta connection.

The star connection requires the use of three transformers, and if any one transformer becomes fault or disabled, the whole group might become disabled. Nevertheless, the star connected three phase transformer is especially convenient and economical in electrical power distributing systems, in that a fourth wire may be connected as a neutral point, ( n ) of the three star connected secondaries as shown.

Transformer Star and Star Connections

The voltage between any line of the three-phase transformer is called the “line voltage”, VL, while the voltage between any line and the neutral point of a star connected transformer is called the “phase voltage”, VP. This phase voltage between the neutral point and any one of the line connections is 1/√3 × VL of the line voltage. Then above, the primary side phase voltage, VP is given as.

The secondary current in each phase of a star-connected group of transformers is the same as that for the line current of the supply, then IL = IS.

Then the relationship between line and phase voltages and currents in a three-phase system can be summarised as:

Three-phase Voltage and Current

Connection Phase Voltage Line Voltage Phase Current Line Current

Star VP = VL ÷ √3 VL = √3 × VP IP = IL IL = IP

Delta VP = VL VL = VP IP = IL ÷ √3 IL = √3 × IP

Where again, VL is the line-to-line voltage, and VP is the phase-to-neutral voltage on either the primary or the secondary side.

Other possible connections for three phase transformers are star-delta Yd, where the primary winding is star-connected and the secondary is delta-connected or delta-star Dy with a delta-connected primary and a star-connected secondary.

Delta-star connected transformers are widely used in low power distribution with the primary windings providing a three-wire balanced load to the utility company while the secondary windings provide the required 4th-wire neutral or earth connection.

When the primary and secondary have different types of winding connections, star or delta, the overall turns ratio of the transformer becomes more complicated. If a three-phase transformer is connected as delta-delta ( Dd ) or star-star ( Yy ) then the transformer could potentially have a 1:1 turns ratio. That is the input and output voltages for the windings are the same.

However, if the 3-phase transformer is connected in star–delta, ( Yd ) each star-connected primary winding will receive the phase voltage, VP of the supply, which is equal to 1/√3 × VL.

Then each corresponding secondary winding will then have this same voltage induced in it, and since these windings are delta-connected, the voltage 1/√3 × VL will become the secondary line voltage. Then with a 1:1 turns ratio, a star–delta connected transformer will provide a √3:1 step-down line-voltage ratio.

Then for a star–delta ( Yd ) connected transformer the turns ratio becomes:

Star-Delta Turns Ratio

Likewise, for a delta–star ( Dy ) connected transformer, with a 1:1 turns ratio, the transformer will provide a 1:√3 step-up line-voltage ratio. Then for a delta-star connected transformer the turns ratio becomes:

Delta-Star Turns Ratio

Then for the four basic configurations of a three-phase transformer, we can list the transformers secondary voltages and currents with respect to the primary line voltage, VL and its primary line current IL as shown in the following table.

Three-phase Transformer Line Voltage and Current

Primary-Secondary

Configuration

Line Voltage

Primary or Secondary

Line Current

Primary or Secondary

Delta – Delta

Delta – Star

Star – Delta

Star – Star

Where: n equals the transformers “turns ratio” (T.R.) of the number of secondary windings NS, divided by the number of primary windings NP. ( NS/NP ) and VL is the line-to-line voltage with VP being the phase-to-neutral voltage.

Three Phase Transformer Example

The primary winding of a delta-star ( Dy ) connected 50VA transformer is supplied with a 100 volt, 50Hz three-phase supply. If the transformer has 500 turns on the primary and 100 turns on the secondary winding, calculate the secondary side voltages and currents.

Given Data: transformer rating, 50VA, supply voltage, 100v, primary turns 500, secondary turns, 100.

Then the secondary side of the transformer supplies a line voltage, VL of about 35v giving a phase voltage, VP of 20v at 1.44 amperes.

Three Phase Transformer Construction We have said previously that the three-phase transformer is effectively three interconnected single phase transformers on a single laminated core and considerable savings in cost, size and weight can be achieved by combining the three windings onto a single magnetic circuit as shown.

A three-phase transformer generally has the three magnetic circuits that are interlaced to give a uniform distribution of the dielectric flux between the high and low voltage windings. The exception to this rule is a three-phase shell type transformer. In the shell type of construction, even though the three cores are together, they are non-interlaced.

Three Phase Transformer Construction

The three-limb core-type three-phase transformer is the most common method of three-phase transformer construction allowing the phases to be magnetically linked. Flux of each limb uses the other two limbs for its return path with the three magnetic flux’s in the core generated by the line voltages differing in time-phase by 120 degrees. Thus the flux in the core remains nearly sinusoidal, producing a sinusoidal secondary supply voltage.

The shell-type five-limb type three-phase transformer construction is heavier and more expensive to build than the core-type. Five-limb cores are generally used for very large power transformers as they can be made with reduced height. A shell-type transformers core materials, electrical windings, steel enclosure and cooling are much the same as for the larger single-phase types.

The Current Transformer

Current Transformer Basics The Current Transformer ( C.T. ), is a type of “instrument transformer” that is designed to produce an alternating current in its

secondary winding which is proportional to the current being measured in its primary.

Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a standard ammeter. The principal of operation of a current transformer is no different from that of an ordinary transformer.

Typical Current Transformer

Unlike the voltage or Power Transformer looked at previously, the current transformer consists of only one or very few turns as its primary winding. This primary winding can be of either a single flat turn, a coil of heavy duty wire wrapped around the core or just a conductor or bus bar placed through a central hole as shown.

Due to this type of arrangement, the current transformer is often referred too as a “series transformer” as the primary winding, which never has more than a very few turns, is in series with the current carrying conductor.

The secondary winding may have a large number of coil turns wound on a laminated core of low-loss magnetic material which has a large cross-sectional area so that the magnetic flux density is low using much smaller cross-sectional area wire, depending upon how much the current must be stepped down. This secondary winding is usually rated at a standard 1 Ampere or 5 Amperes for larger ratings.

There are three basic types of current transformers: “wound”, “toroidal” and “bar”.

• Wound current transformers – The transformers primary winding is physically connected in

series with the conductor that carries the measured current flowing in the circuit. The magnitude

of the secondary current is dependent on the turns ratio of the transformer.

• Toroidal current transformers – These do not contain a primary winding. Instead, the line that

carries the current flowing in the network is threaded through a window or hole in the toroidal

transformer. Some current transformers have a “split core” which allows it to be opened, installed,

and closed, without disconnecting the circuit to which they are attached.

• Bar-type current transformers – This type of current transformer uses the actual cable or bus-

bar of the main circuit as the primary winding, which is equivalent to a single turn. They are fully

insulated from the high operating voltage of the system and are usually bolted to the current

carrying device.

Current transformers can reduce or “step-down” current levels from thousands of amperes down to a standard output of a known ratio to either 5 Amps or 1 Amp for normal operation. Thus, small and accurate instruments and control devices can be used with CT’s because they are insulated away from any high-voltage power lines. There are a variety of metering applications and uses for current transformers such as with Wattmeter’s, power factor meters, watt-hour meters, protective relays, or as trip coils in magnetic circuit breakers, or MCB’s.

Current Transformer

Generally current transformers and ammeters are used together as a matched pair in which the design of the current transformer is such as to provide a maximum secondary current corresponding to a full-scale deflection on the ammeter. In most current transformers an approximate inverse turns ratio exists between the two currents in the primary and secondary windings. This is why calibration of the CT is generally for a specific type of ammeter.

Most current transformers have a the standard secondary rating of 5 amps with the primary and secondary currents being expressed as a ratio such as 100/5. This means that the primary current is 100 times greater than the secondary current so when 100 amps is flowing in the primary conductor it will result in 5 amps flowing in the secondary winding, or one of 500/5 will produce 5 amps in the secondary for 500 amps in the primary conductor, etc.

By increasing the number of secondary windings, N2, the secondary current can be made much smaller than the current in the primary circuit being measured because as N2 increases, I2 goes down by a proportional amount. In other words, the number of turns and the current in the primary and secondary windings are related by an inverse proportion.

We know from our tutorial on double wound voltage transformers that its turns ratio is equal to:

from which we get:

As the primary usually consists of one or two turns whilst the secondary can have several hundred turns, the ratio between the primary and secondary can be quite large. For example, assume that the current rating of the primary winding is 100A. The secondary winding has the standard rating of 5A. Then the ratio between the primary and the secondary currents is 100A-to-5A, or 20:1. In other words, the primary current is 20 times greater than the secondary current.

It should be noted however, that a current transformer rated as 100/5 is not the same as one rated as 20/1 or subdivisions of 100/5. This is because the ratio of 100/5 expresses the “input/output current rating” and not the actual ratio of the primary to the secondary currents. Also note that the number of turns and the current in the primary and secondary windings are related by an inverse proportion.

But relatively large changes in a current transformers turns ratio can be achieved by modifying the primary turns through the CT’s window where one primary turn is equal to one pass and more than one pass through the window results in the electrical ratio being modified.

So for example, a current transformer with a relationship of say, 300/5A can be converted to another of 150/5A or even 100/5A by passing the main primary conductor through its interior window two or three times as shown. This allows a higher value current transformer to provide the maximum output current for the ammeter when used on smaller primary current lines.

Current Transformer Primary Turns Ratio

Current Transformer Example No1 A bar-type current transformer which has 1 turn on its primary and 160 turns on its secondary is to be used with a standard range of ammeters that have an internal resistance of 0.2Ω’s. The ammeter is required to give a full scale deflection when the primary current is 800 Amps. Calculate the maximum secondary current and secondary voltage across the ammeter.

Secondary Current:

Voltage across Ammeter:

We can see above that since the secondary of the current transformer is connected across the ammeter, which has a very small resistance, the voltage drop across the secondary winding is only 1.0 volts at full primary current. If the ammeter is removed, the secondary winding becomes open-circuited and the transformer acts as a step-up transformer due to the very large increase in magnetising flux in the secondary core. This results in a high voltage being induced in the secondary winding equal to the ratio of: Vp(Ns/Np) being developed across the secondary winding.

So for example, assume our current transformer from above is used on a 480 volt three-phase power line. Therefore:

This 76.8kV is why a current transformer should never be left open-circuited or operated with no-load attached when the main primary current is flowing through it. If the ammeter is to be removed, a short-circuit should be placed across the secondary terminals first to eliminate the risk of shock.

This is because when the secondary is open-circuited the iron core of the autotransformer operates at a high degree of saturation, which produces an abnormally large secondary voltage, and in our simple example above, this was calculated at 76.8kV!. This high secondary voltage could damage the insulation or cause electric shock if the CT’s terminals are accidentally touched.

Handheld Current Transformers

There are many specialized types of current transformers now available. A popular and portable type which can be used to measure circuit loading are called “clamp meters” as shown.

Clamp meters open and close around a current carrying conductor and measure its current by determining the magnetic field around it, providing a quick measurement reading usually on a digital display without disconnecting or opening the circuit.

As well as the handheld clamp type CT, split core current transformers are available which has one end removable so that the load conductor or bus bar does not have to be disconnected to install it. These are available for measuring currents from 100 up to 5000 amps, with square window sizes from 1″ to over 12″ (25-to-300mm).

Then to summarise, the Current Transformer, (CT) is a type of instrument transformer used to convert a primary current into a secondary current through a magnetic medium. Its secondary winding then provides a much reduced current which can be used for detecting overcurrent, undercurrent, peak current, or average current conditions.

A current transformers primary coil is always connected in series with the main conductor giving rise to it also being referred to as a series transformer. The nominal secondary current is rated at 1A or 5A for ease of measurement. Construction can be one single primary turn as in Toroidal, Doughnut, or Bar types, or a few wound primary turns, usually for low current ratios.

Current transformers are intended to be used as proportional current devices. Therefore a current transformers secondary winding should never be operated into an open circuit, just as a voltage transformer should never be operated into a short circuit.

Very high voltages will result from open circuiting the secondary circuit of an energized CT so their terminals must be short-circuited if the ammeter is to be removed or when a CT is not in use before powering up the system.

In the next tutorial about Transformers we will look at what happens when we connect together three individual transformers in a star or delta configuration to produce a larger power transformer called a Three Phase Transformer used to supply 3-phase supplies.

Understanding Vector Group of Transformer (1)

Understanding Vector Group of Transformer

Introduction

Three phase transformer consists of three sets of primary windings, one for each phase, and three sets of secondary

windings wound on the same iron core.

Separate single-phase transformers can be used and externally interconnected to yield the same results as a 3-phase

unit.

The primary windings are connected in one of several ways. The two most common configurations are the delta, in

which the polarity end of one winding is connected to the non-polarity end of the next, and the star, in which all

three non-polarities (or polarity) ends are connected together. The secondary windings are connected similarly. This

means that a 3-phase transformer can have its primary and secondary windings connected the same (delta-delta or

star-star), or differently (delta-star or star-delta).

It’s important to remember that the secondary voltage waveforms are in phase with the primary waveforms when

the primary and secondary windings are connected the same way. This condition is called “no phase shift.”

But when the primary and secondary windings are connected differently, the secondary voltage waveforms will

differ from the corresponding primary voltage waveforms by 30 electrical degrees. This is called a 30 degree phase

shift. When two transformers are connected in parallel, their phase shifts must be identical; if not, a short circuit will

occur when the transformers are energized.”

Basic Idea of Winding

An ac voltage applied to a coil will induce a voltage in a second coil where the two are linked by a magnetic path.

The phase relationship of the two voltages depends upon which ways round the coils are connected. The voltages

will either be in-phase or displaced by 180 degree.

When 3 coils are used in a 3 phase transformer winding a number of options exist. The coil voltages can be in phase

or displaced as above with the coils connected in star or delta and, in the case of a star winding, have the star point

(neutral) brought out to an external terminal or not.

Six Ways to wire Star Winding:

Six Ways to wire Star Winding

Six Ways to wire Delta Winding:

Six Ways to wire Delta Winding

Polarity

An AC voltage applied to a coil will induce a voltage in a second coil where the two are linked by a magnetic path.

The phase relationship of the two voltages depends upon which way round the coils are connected. The voltages

will either be in-phase or displaced by 180 deg.

When 3 coils are used in a 3 phase transformer winding a number of options exist. The coil voltages can be in phase

or displaced as above with the coils connected in star or delta and, in the case of a star winding, have the star point

(neutral) brought out to an external terminal or not.

Additive and substractive polarity of

transformer

When Pair of Coil of Transformer have same direction than voltage induced in both coil are in same direction from

one end to other end. When two coil have opposite winding direction than Voltage induced in both coil are in

opposite direction.

Winding connection designations

First Symbol: for High Voltage: Always capital letters.

D=Delta, S=Star, Z=Interconnected star, N=Neutral

Second Symbol: for Low voltage: Always Small letters.

d=Delta, s=Star, z=Interconnected star, n=Neutral.

Third Symbol: Phase displacement expressed as the clock hour number (1,6,11)

Example–Dyn11Transformer has a delta connected primary winding (D) a star connected secondary (y) with the star point brought

out (n) and a phase shift of 30 deg leading (11).

The point of confusion is occurring in notation in a step-up transformer. As the IEC60076-1 standard has stated, the

notation is HV-LV in sequence. For example, a step-up transformer with a delta-connected primary, and star-

connected secondary, is not written as ‘dY11′, but ‘Yd11′. The 11 indicates the LV winding leads the HV by 30

degrees.

Transformers built to ANSI standards usually do not have the vector group shown on their nameplate and instead a

vector diagram is given to show the relationship between the primary and other windings.

Vector Group of Transformer

The three phase transformer windings can be connected several ways. Based on the windings’ connection, the vector

group of the transformer is determined.

The transformer vector group is indicated on the Name Plate of transformer by the manufacturer. The vector

group indicates the phase difference between the primary and secondary sides, introduced due to that particular

configuration of transformer windings connection.

The Determination of vector group of transformers is very important before connecting two or more transformers in

parallel. If two transformers of different vector groups are connected in parallel then phase difference exist between

the secondary of the transformers and large circulating current flows between the two transformers which is very

detrimental.

Phase Displacement between HV and LV Windings

The vector for the high voltage winding is taken as the reference vector. Displacement of the vectors of other

windings from the reference vector, with anticlockwise rotation, is represented by the use of clock hour figure.

IS: 2026 (Part 1V)-1977 gives 26 sets of connections star-star, star-delta, and star zigzag, delta-delta, delta star,

delta-zigzag, zigzag star, zigzag-delta. Displacement of the low voltage winding vector varies from zero to -330° in

steps of -30°, depending on the method of connections.

Hardly any power system adopts such a large variety of connections. Some of the commonly used connections

with phase displacement of 0, ‐300, ‐180″ and ‐330° (clock‐hour setting 0, 1, 6 and 11).

Symbol for the high voltage winding comes first, followed by the symbols of windings in diminishing sequence of

voltage. For example a 220/66/11 kV Transformer connected star, star and delta and vectors of 66 and 11 kV

windings having phase displacement of 0° and -330° with the reference (220 kV) vector will be represented As Yy0

– Yd11.

The digits (0, 1, 11 etc) relate to the phase displacement between the HV and LV windings using a clock face

notation. The phasor representing the HV winding is taken as reference and set at 12 o’clock. Phase rotation is

always anti-clockwise. (International adopted).

Use the hour indicator as the indicating phase displacement angle. Because there are 12 hours on a clock, and a

circle consists out of 360°, each hour represents 30°.Thus 1 = 30°, 2 = 60°, 3 = 90°, 6 = 180° and 12 = 0° or 360°.

The minute hand is set on 12 o’clock and replaces the line to neutral voltage (sometimes imaginary) of the HV

winding. This position is always the reference point.

Example

Digit 0 =0° that the LV phasor is in phase with the HV phasor

Digit 1 =30° lagging (LV lags HV with 30°) because rotation is anti‐clockwise.

Digit 11 = 330° lagging or 30° leading (LV leads HV with 30°)

Digit 5 = 150° lagging (LV lags HV with 150°)

Digit 6 = 180° lagging (LV lags HV with 180°)

When transformers are operated in parallel it is important that any phase shift is the same through each. Paralleling

typically occurs when transformers are located at one site and connected to a common bus bar (banked) or located at

different sites with the secondary terminals connected via distribution or transmission circuits consisting of cables

and overhead lines.

Phase Shift (Deg) Connection

0 Yy0 Dd0 Dz0

30 lag Yd1 Dy1 Yz1

60 lag

Dd2 Dz2

120 lag

Dd4 Dz4

150 lag Yd5 Dy5 Yz5

180 lag Yy6 Dd6 Dz6

150 lead Yd7 Dy7 Yz7

120 lead

Dd8 Dz8

60 lead

Dd10 Dz10

30 lead Yd11 Dy11 Yz11

The phase-bushings on a three phase transformer are marked either ABC, UVW or 123 (HV-side capital, LV-side

small letters). Two winding, three phase transformers can be divided into four main categories

Group O’clock TC

Group I 0 o’clock, 0° delta/delta, star/star

Group II 6 o’clock, 180° delta/delta, star/star

Group III 1 o’clock, ‐30° star/delta, delta/star

Group IV 11 o’clock, +30° star/delta, delta/star

Minus indicates LV lagging HV, plus indicates LV leading HV

ClockNotation0(PhaseShift0)

Clock Notation 0 (Phase Shift 0)

ClockNotation1(PhaseShift‐30)

Clock Notation 1 (Phase Shift ‐30)

ClockNotation2(PhaseShift‐60)

Clock Notation 2 (Phase Shift ‐60)

ClockNotation4(PhaseDisplacement‐120)

Clock Notation 4 (Phase Displacement ‐

120)

ClockNotation5(PhaseDisplacement‐150)

Clock Notation 5 (Phase Displacement ‐150)

ClockNotation6(PhaseShift+180)

Clock Notation 6 (Phase Shift +180)

ClockNotation7(PhaseShift+150)

Clock Notation 7 (Phase Shift +150)

ClockNotation11(PhaseShift+30)

Clock Notation 11 (Phase Shift +30)