10_power supply sys

8/6/2019 10_Power Supply Sys

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10POWER SUPPLY SYSTEM

Power Supply system forms an essential part of any installation. It is planned to take care ofthe entire load of the installation.

POWER SUPPLY DISTRIBUTION

No power supply system is complete unless it has the necessary switch gear etc. to protectthe equipment from over voltages, under voltages, short unit currents etc. In order to ensurecontinuous working of an installation D/G sets are provided to generate supply to the eventof failure of mains supply. A power supply schematic of an FM transmitter non cosited withMP studio is shown in figure. 1.

Fig. 1 Power Supply Schematic (FM Transmitter Non-cosited)

The incoming supply that is received from the Electric corporations is 11 kV 3 phase A/C ingeneral. This supply is stepped down to 440 volt 3 phase LT supply making use of 150/100kVA, 11 KV/400 V, step down transformer.

It is always preferred to have two H.T. feeders coming to an installation from two separatesources so as to always have 100% standby supply coming to the station.

It is a common feature to make use of HT isolators in each H.T. feeder so that supply of asingle feeder can be made use of at a time.

STI(T) Publication 97 007/2003


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FM Transmitter

The outputs of two transformers are brought on the L.T. bus bar through the MCCBs of 200Amp. Rating which are electrically and mechanically interlocked with each other.

The supply to the essential equipment is fed though a changeover switch between the D/Gsupply and mains supply.

The bus bar is always provided with various meters to monitor the current and voltages ondifferent phases.

COMBINING UNIT CONROL CIRCUIT AND PATCH PANEL

The FM Transmitters used in our network are mostly of M/s. BEL or GCEL make. In the caseof Transmitters of M/s. GCEL make 3 phase supply as available from the switch room isdirectly extended to the transmitter and no interlock circuit has been introduced. However, inthe case of BEL Transmitters an elaborate interlock circuit has been used which needs a

thorough study.

The transmitter combining unit provides for :

(i) Summing up of the powers of the individual transmitters and transfer of the sameeither to the Antenna or the Dummy load.

(ii) The Transfer of the power of one of the Transmitters to the antenna and that ofthe other to the Dummy Load and vice versa.

In order to facilitate selection of the transmitters in any one of these modes, an elaboratearrangement of U-links is provided on the body of the combining unit rack.

The U-links operate micro switches which in turn operate relays numbered K1 to K9.

A mimic diagram is given on the body of the rack for reference by the operational staff.

The various relays that are operated with transmitters selected in different modes are asunder :-

S.No. Mode Relays that operate

(1) TXR (A+B) on Antenna K1, K4, K6, K8(2) TXR (A+B) on Dummy Load K2, K4, K6, K8(3) TXR A on Dummy Load

TXR B on Antenna K1, K3, K7(4) TXR A on Antenna

TXR B on Dummy Load K1, K5, K9

The schematic of the control circuit and patch panel of combining unit is given in Fig. 2.



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Power Supply System

Fig.

2CombiningUnit-ControlcircuitandPatchPanel



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FM Transmitter

Salient points of the control circuit of the combining unit :-

(1) With transmitters selected in any mode, the U-links extend + 24 volt supply to therelays K1 to K9 and some of these operate depending on the patching of thevarious U-links on the body of the combining rack.

(2) The combining rack of the 2 x 3 kW Transmitters has the necessary switch panelon its body for putting on each one of the two transmitters.

(3) When the transmitter control switch is put in the standby position, both thetransmitters are energized. However, RF remains disabled in this position. Bothtransmitters give the rated output when the control switch is put in ON position.

It is necessary to understand the working of the control circuit of the combining unit.

(a) The single phase 240 volt AC supply from the supply distribution board is firstcoming on the circuit breaker CB1. The cooling fan operates when CB1 is put on.This supply goes to the step down transformer T1. 24 volt supply available from

the rectifier systems is used for activating the relays and lamps.

(b) The mains to the Reject Load is extended directly from the circuit breaker CB1.

(c) +24 V supply is directly given to one end of each of the two relays i.e. K10 andK11. The circuit of the two relays i.e. K10 and K11 is completed through the closingcontacts of particular combination of relays K1 K9 which operate depending onthe mode in which the transmitters are selected to work.

(d) With the operation of relay K10, relay K14 also operates.

(e) When the control switch is put in Standby position, +24 volt supply is extended

to one end of the relay K15 through the N/O contact of K14 relay and the relay K15is operated.

(f) As the relay K15 operates, the relays K16 and K17 are operated subsequently. Thetwo relay extend the 3 phase supply coming from the MDB to each one of the twotransmitters A & B.

(g) Relay K18 operates through the loop back circuit of the transmitter.

(h) The relay K19 operates through the contact of K18 when the transmitter is put inON position.

(i) The N/O contacts of relay K19 when closed Put through the carrier enable signalto each transmitter.

(j) The relay K12 operates in the event of operation of any one of the relays K2, K3 orK9 when it is required that the Power should be terminated on the dummy load.

(k) When K12 relay operates, K13 is operated subsequently extending the supply tothe Dummy Load.

The 3 phase supply extended to both the transmitters from the combiner unit is furtherdistributed as per the schematic shown in Figure 3.

FM Transmitter operates from 415 V 3-phase power supply. The unregulated 3-phasesupply from the mains is connected to Mains Distribution panel (MDP) provided with usual



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Power Supply System

facilities of switching and metering. From the MDP, the regulated supply is routed to anAutomatic Voltage Regulator (AVR) of 50 kVA capacity and the regulated output from theAVR is taken back to the MDP where it is further distributed to the two transmitters A & Bvia the combining unit.

Power supply distribution of 2 x 3 kW FM transmitter is shown in Fig.3. The automatic cutoutQ1 on the front panel switches in the 3-phase supply to transformer trolley A14A and Q2energises the phase monitor (or phase watcher) which activates the control system in caseof a phase failure. Two phases U and V are taken from the output of phase monitor tooperate either relay K1A or K2A. The contacts of K1A and K2A are used in such a way thatat a time one out of the two phases is available on the U/V line for energizing the controlsystem and other sub-units of the transmitter. If the selected phase fails, the inactive relayK1A or K2A will operate and the second phase will become available on U/V line. If K1Aoperates first, phase U will be available and if K2A operate first, phase V will be available onU/V line. When the relay K1A or K2A operates, the 240 V supply is extended (please referDrg. No. 746.4105.01 FS, sheet 4) to :

1. Fuse F15A for blower A.2. Fuse F16A for blower B (from power panel B).3. Absorber fan through fuse F11A.4. Exciter and FKDL via terminal block X52.5. Mains transformer T1 A (mounted on the hinged power Panel A) via fuse F12.

The mains transformer T1 has the following secondary voltages :-

1. 24 V AC for RF and AF switches through terminal points X49A & X50A on therear of rack. This is converted into + 24V DC in the Adapter Unit. (Refer Drg.No. 746.4105.01 FS, sheet 3).

2. 16 V AC for voltage Regulator A11A which has two outputs of + 18 V (P2A) and +12 V (P3A).

3. 16 V AC for voltage regulator A 12A which has an output of 12 V (N3A).

4. 21V AC for generating unregulated voltage of + 24V (P1A) with diode V11A andcondenser C114.

DISTRIBUTION OF VOLTAGES TO VARIOUS SUB-UNITS

(Reference Fig. 3 and Drg. No. 746.4105.01 FS sheets 3 & 4)

S.No. Sub-Unit Voltage Available Remarks

1. Switch-oncontrol Unit

+ 12 V Regulated

- 12 V Regulated

From Power panels A & B.

2. Exciter A 230 V mains from powerpanel A

Exciter has a built-in powersupply for generating DCvoltages of +12 V, + 24 V &+ 5 V.

3. Exciter B 230 V mains from powerpanel B.

Exciter has a built-in powersupply for generating DC

voltages of +12 V, + 24 V &+ 5 V.



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FM Transmitter

4. VHF Poweramplifiers oftransmitter A

+ 28 V for collector supply+ 12 V regulator for monitor

From Transformer Trolley AFrom power panel A

5. VHF Poweramplifiers oftransmitter B

+ 28 V for collector supply+ 12 V regulator for monitor

From Transformer Trolley BFrom power panel B

6. Blower controlcircuit

+ 12 V regulated+ 24 V unregulated

From power panel AFrom power panel B

7. Adapter Unit 24 V AC Input+ 24 V DC output

From panels A & B foroperation of RF and AFswitch.

8. MonitoringDemodulator(FKDL)

230 V mains input It has built in regulatedsupply.

9. Absorber unit + 24 V unregulated

10. Signal Board + 12 V regulated

REDUNDANCY

If one of the power panel fails or if P1(+24 V) or P3(+12 V) or N3(-12 V) fails in one of thetransmitters due to some reason, still the other transmitter can be energized and put on the airbecause P1, P3 and N3 of both the power panels have been paralleled in the adapter unit asfollows :-

P1A and P1B Via pins X4L. 17 d and 18 d

P3A and P3B Via pins X4L. 17 c and 18 c

N3A and N3B via pins X4L 17 a and 18 a

MA and MB (Grounds) via pins X4L. 17 b and 18 b.

Thus the operation of Switch-on Unit, adapter, Blower control circuit, Signal Board and sub-units of Power Amplifiers, absorber etc. in case of failure of one or more of above supplies isensured by making available P1, P3 and N3 from the other power panel to these units.Similarly, the + 24 V DC output of rectifiers V21 and V31 in adapter unit have been

paralleled to ensure the operation or RF and AF switches under such circumstances. (ReferDrg. No. 746.4105.01 FS sheet 3).

Exciter A gets its mains supply from Power Supply panel A where as Exciter B gets frompanel B. FKDL gets mains supply from panel A.



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Power Supply System

Fig. 3 Power Supply Distribution of 2 x 3 kW FM Transmitter

Power Amplifiers of Transmitter A gets supply of + 28V from Trafowagen of Transmitter A

(mounted on front) whereas power amplifiers of Transmitter B get the supply fromTrafowagen of Transmitter B (mounted on rear).



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FM Transmitter

IMPORTANT POINTS

- Distribution of voltages in power panel B and sub-unit of transmitter B is identical

except that it does not contain the control circuit for two blowers and absorber fan.This circuit is mounted on Power Panel A.

- Transformer trolleys for the two transmitters are interchangeable although connectorsX31 and X51 are loose in TXA and are mounted on Panel in TXB.

- Voltages check points are available on the rear side below the RF switch as follows

Connector No. Voltage

a) X49A, X50A (TX A) 24 V ACX49B,X50B(TXB)

b) X45A, X45B + 24V DC (Unregulated)c) X43A, X43B - 12 V (Regulated)d) X41A, X41B + 12 V (Regulated)

- Operating status/faults are indicated by LEDs/Neon lamps mounted on the two powerpanels as follows :

POWER PANEL A

H15A Lights up when fuse F15A for blower A(RED) blows OFF or is removed manually.

H16A Lights up when fuse F16A for blower B.(RED) blows OFF or is removed manually.H11A Lights up when fuse F11A for absorber fan

Blows OFF or is removed manually.LED H1A Failure of + 12 V supply(RED)LEDH2A Failure of 12 V supply(RED)LED H3A Failure of one or more power phases.LED H4A Failure in AC switch over (mismatch of transformer tappings)H5 Changeover to standby blower completed

(RED)H6 (Yellow) Fault in air flow

POWER PANEL B

LED H1B Failure of + 12 V supplyLED H2B Failure of 12 V supplyLED H3B Failure of one or more power phases.LED H4B Fault in AC switchover (mismatch of transformer

tappings)



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Power Supply System

PHASE MONITOR

It monitors the condition of the three phases and is a sealed unit. Its inner details are not

known. It responds when one or more phases are faulty or when the voltage is below itsnominal value. This is very sensitive relay and should not be continuously overloaded (atnominal freq) for more than 1.2 times the nominal voltage.

Power reduction results when one phase fails and RF output power becomes 1.7 kW for a 2x 3 kW FM transmitter and 1 kW for a 3 kW FM transmitter. This power reduction can beadjusted by trimming R7 of AGC voltage board (679.2900S).

VOLTAGE REGULATOR

The + 28 V DC supply is obtained by 3-phase rectification and filtering from the twosecondaries of the 3-phase transformer mounted on the transformer trolley. This DC supplyis not regulated thereby resulting in a lot of energy saving. However, the AC primaryvoltages of the transformer are maintained constant within certain limits of variation of ACsupply voltage by automatically changing the taps on the primary side with the help of ACrelays K10 to K14 (mounted on the transformer trolley). Proper operation of these relays isachieved with the help of control circuit called AC supply switchover or line switchover.(Drg. No. 679.5\60355).

AC SUPPLY SWITCH OVER

The 28 V DC supply to the power amplifiers is obtained by 3 phase rectification as shown infigure 4 and 5. Three connections are made to each of the three primary of the 3 phase

transformer one each for over, under and rated voltage. Depending on the AC inputvoltage, contactors switch the voltage to the appropriate set of transformer tapings.Changing the connection on the primary windings by one step results in change in DC outputvoltage by 1 V.

If the AC voltage has its nominal value, contactor K12 operates and applies the a.c. voltageto the middle tap of the three selected taps of each of the primary windings. Contactors K11and K13 operate in case of under voltage and over voltage respectively. The contactors areinterlocked in such a manner that only one contactor can operate at a time.

In order to limit the transient start up current during initial switch on and thus to preventheavy current flow through the rectifiers and also to prevent unwanted operation of the cut

outs etc. R11, R12 and R13 are brought in circuit in the initial phase. The switch over contactorK10 operates after some specified delay and they are bypassed. Simultaneously thecontacts 13-14 of K10 relay close, closing the RF loop thereby enabling the carrier in theExciter.

The contactor K14 is activated for a period beginning shortly before and ending shortly afterthe switchover. AC voltage thus continues to be applied to the transformer duringswitchover through dropping resistors R21, R22 and R23.

In order to know as to how the actual circuit works, we may refer to the circuit given inFigure-5.



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FM Transmitter

Preparation for use

The coding links on the board permit the following settings:

X20 to X2.1-2 Automatic switchover for deviations of more than about 10%

from nominal value.X2. 2-3 Automatic switchover for deviations of more than about 5%

from nominal value.

X30 Settings same as for X20. Hysteresis can be set to thof the window width.

X40 to X4.1-2 Operation with automatic switchover of the inputconnections.

X4.2-3 Automatic switchover disabled.

With an input of the nominal voltage the window centre is adjusted with R5 at MP1. TheLED display H2 Within lights.

The a.c. line voltage is monitored with the use of a window discriminator. The regulation ofthe AC supply is improved so that 28 volt d.c. supply given to the VHF amplifiers that comesdirectly from the rectifier and circuits without regulation is stable and steady.

The window discriminator U1 functions as a sensor for AC supply switch over. It analysesthe height of the input voltage at U1.6,7.

The one half window width is set at U1.9 with R7 and R8 (10% deviation) or R7, R9 (5%Deviation).

The window centre is set with R5 at U1.8 (MP1). This is equal to the actual voltage at MP2

when nominal voltage is present at X1.4. A voltage proportional to the unregulated DCvoltage is applied at X1.4. A fixed reference voltage is +8V set at U1.10 with the help ofresistance R35.

When the input voltage is normal, U1.13 is low.

However when the input voltage is not normal, U1.2 or U1.14 become low. Simultaneously U1.3is also low. This switches R10 or R25 parallel to R8 or R9 thus narrowing the pulse width andgenerating the hysteresis for reverse switch over. We may discuss the different cases oneby one.

When the input voltage at X1.4 is normal, U1.13 becomes low. The indicator lamp H2 lights up.

With the nominal input voltage, the K12 contactor on the transformer trolley is actuated.

With the switch on command from the transmitter, X1.19 goes high. C6 is charged throughR20. When the voltage on C6 reaches 7.5 volts, transistor V53 conducts and activates relayK3. The contactor K10 is actuated by the closing contacts 4-5 of K3. The contactor shortsout the voltage dropping resistance on the transformer trolley.

Now let us presume that the voltage has increased above normal value. U1.2 is low and bothU1.14 and U1.13 are high. The discriminator assumes this state after the switch over.



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FM Transmitter

Fig. 4 Transformer Trolley



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Power Supply System


Fig.

5AC

SupplySwitchover


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FM Transmitter

TRANSFORMER TROLLEY (TRAFOWAGON)

The transformer trolley supplies the required DC voltage for four (5 kW) VHF- amplifier

modules.

i) Description

The transformer is of sturdy construction and, after loosening a retaining screw, it can berolled out of the transmitter rack. It comprises the three-phase transformer, rectifiers withheat sinks, filter chokes and capacitors, as well as the contactors for switching on the ACsupply and selecting a set of tappings.

The power leads and control cables are connected to the 5-kW transformer trolley by meansof connectors manually and to the 3-kW and 1.5-kW trolley through self-engaging

connectors. Lines carrying hazardous voltages are shielded with rigid protective covers.The rectified secondary voltage is led via heavy-duty screw terminals and high-currentcables to the VHF amplifiers.

Voltage-dropping resistors prevent the tripping of the automatic cutouts during switch-on andprotect the rectifiers against excessive current transients.

ii) Specifications

Input voltage : 380 V 3-phase

Control voltage for contactors : 24 V AC

Max. nominal current per filter unit : Approx. 120 A

Output voltage : Approx. 20 to 28 V

iii) Preparation For Use

The leads to the VHF amplifiers are connected to the transformer DC outputs C1.1/2,C2.1/2, C3.1/2 and C4.1/2. The correct polarity of the connections must be observed.

Three connections are made to each of the three primary windings of the 3-phase

transformer one each for over-, under-, and rated voltage. Depending on the AC inputvoltage, contactors switch the voltage to the appropriate set of transformer terminals.

iv) Adjustment Of Operating Voltage

When the transmitter is first placed in operation, the following connections on the primaryside of the 3-phase transformer are provisionally made:



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Power Supply System

U-winding: W16 to terminal 4 (for overvoltage)W13 5 (for rated voltage)W10 6 or 7 (for undervoltage)

V-winding W17 to terminal 4

W14 5W11 6 or 7

W-winding: W18 to terminal 4W15 5W12 6 or 7

Changing the connection to the primary windings by one step changes the DC outputvoltage by approximately 1 V. Depending on the transmitter power, tapping connections arechanged to higher or lower-numbered terminals as required.

Following this, roll the transformer trolley into the rack and fasten the retaining screw and

plug in the two connectors X31 and X51.

v) Filter Circuits

The transformer has four mutually isolated secondary output windings.

Each 3-phase rectifier set is made up of individual rectifier modules V1 to V6 and V11 to V16.Heat developed in these modules is dissipated through a heat sink. The RC networks Z1 toZ6 and Z11 to Z16 protect the rectifiers against voltage peaks. The chokes and filteringcapacitors filter out the residual hum of the rectifier circuits. The shunt resistors at the outputhave the function of discharging the capacitors.

vi) Repair And Adjustments

If a rectifier module is replaced, the heat-conducting paste should be washed off withalcohol. A thin coat of heat-conducting paste should be applied to the new module.

The output voltage of the filter units is determined by the selection of primary tapings. Anychange in these connections must be made uniformly on all three transformer windings.

12 V REGULATOR

The voltage regulator has the function of supplying 12V to the regulating , monitoring and

indication facilities.

Operating Data

Input Voltage Approx. 20 V ACOutput Voltage 12 VShort-circuit current Approx. 3 A



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FM Transmitter

Circuit Description

Circuit diagram 679.2315 S (Fig. 6).

The input AC voltage is applied to bridge rectifier V11. The DC output is filtered by C1, C2and C3 and applied via fuse F1 to regulator N1, which provides the output voltage,adjustable with R2 to 12 V.

Zener diode V2 provides protection for the regulator input N1.2. Fuse F1 opens when thediode conducts. If an overvoltage occurs at the output of the regulator, as result of a defectin the latter, diode V5 becomes conducting, and F1 opens in this case also. LED H1 lightsup.

If the output voltage falls below approximately +8 V, V10 turns off and relay K1 drops out.

The K1 contacts serve for floating error-signalling and disabling of the carrier when theauxiliary voltage fails.

The filtered, unregulated 24-V output of the rectifier is made available on terminal X1.a/b30.

A lamp-check button for testing LED H1 can be connected to terminal X1. A/b17.

Adjustment

The value of the output voltage V is determined by the resistance ratio R2/R3:

3RA50V25.1

3R)V25.1V(2R

3RA503R2R125.1V

+

=

+

+=



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Power Supply System


Fig. 6 : 12 Volt Regulator


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FM Transmitter

BLOWER CONTROL SYSTEM

The transmitter provides for Blower switch over in case of fault/failure of one of the blowersand AC supply switch over in case of under voltage and over voltages in the incoming

supply. The blower control circuit is given in figure 7.

The transmitter is equipped with two rack blowers in passive standby configuration. Theblower switch over selects the preferred blower A or B, monitors the airflow and in case offaulty operation, the standby blower takes over from the other blower.

The blower can be switched on by any of the four commands on X1S 4b, 5a, 5b or 6a withH on output D1.1 V3 conducts and switches relay K2. contacts 4-7 of K2 are closed. Inaddition, gate D5 is unlatched and the blower pre-selected by switch S1 is switched on via V1or V2.

Blower A is switched on when D 5-1 is high and V 1 conducts. This is possible when D5 2/3

are high which in turn is possible when S1 1/4 is Low and accordingly D 4-5 is also lowand D4-4 and D5-2/3 is high.

Further more D 5-4 should be high. This is possible when D 1-1 goes high which is possibleonly when there is low at X 15.

Further more D 5-5 should be high. This is possible when D3-10 is high which is itself isonly possible when D 2-1 is low. D2-1 is low when D2-3/2 is also low and D 1-9/10/11/12 ishigh. Such a possibility arises when the contacts K 2-1-4 open.

When S1 is in position AD 4.2 is high with D3.10 also at high, D5-9/10 are low and hence D 5-13 is also low keeping the transistor V2 cut off and blower B accordingly shut off.

In case the preferred blower i.e. A fails or if the pressure decreases, the transistor in themonitor goes out of conduction. The relay K2 is de-energized. Contact K2-1/4 again closeand the display H6 (Airflow Fault) lights up.

The gate inputs D 1-9/10/11/12 become low via V20 and R14 and output D1.13 becomes highwith D 2.2/3/4/5 high, D2.1 is also high capacitor C14 charges through R26.

When the Voltage reaches about 5 V, D3.10 becomes low, D5.1 as well becomes low and thusV1 is turned off.

With D 4-1 low, D4.3 becomes high and with D 5-9/10/11/12 High, V2 starts conducting andswitches on Blower B.

When D3.10 is low, D4.10 becomes High transmitter V4 conducts and the relay K1-2.3operates contacts K1-1.4 close and the indication H5 lights up. An open line to V32 causes ahigh at, indicating a fault with a low signal sent to the Switch on Unit.

Both the blowers can also be operated when S1 is kept in center position. Contacts 2-3 and4-5 are made. Thus D4.2 and D4.5 are low energizing both the blowers via V1 and V2.



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Power Supply System


Fig.

7BlowerControlBoa

rd

10_power supply sys

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