nRF51 high current at connected state.

Question

Hello all,
Before asking question I thotoughly read the previous discussions but it didn't help in my case.
I use nRF51822 rev.2 + SD130 device with NUS service for BLE data exchange.
I have decreased current to 14uA in idle during advertisement. However when I connected to peer central the current consumption increased to about 460-500uA and remains in this range until I disconnect device. I tried to increase connection intervals but no noticable result was received.
I switched off all peripherals to exclude influence of possible bug in code or hardware.
Now I think about HFCLK and 1.2V LDO but didn't found what peripherals use it. Please help with advice or direct to possible wayout. 
 Connection params:
Connection interval: 500-1900ms
Slave latency: 4
Supervision timeout: 20000ms 
 I tried to increase min connection interval but it didn't led to current fall.

Valer_I · Accepted Answer

Dear Stefan Birnir Sverrisson,
Many thanks for your explanation and links but I solved this problem befre read your answer )).
I have seen all these threads you've mentioned and many others to investigate the problem.
I do not use nRF51 sdk due to tight memory budget and use only sd_... functions to communicate with softdevice.
My code is next: 
 err = sd_ble_gap_connect(&current_addr, &c_scan_param, &c_connection_param); 
 
 c_scan_param - here put our desired connection params (as far as I understand here they written to the PPCP characteristic). The central able to read them and use, but on all devices I've try - skip. After connection the connection interval depend on device and is in range 20-100ms. Next I follow bonding routines and it is better to do them on high speed. Than when bonded: 
 }else if (evt_id == BLE_GAP_EVT_AUTH_STATUS){
...
 if (ble_evt->evt.gap_evt.params.auth_status.bonded == 1){
... 
 uint32_t res=sd_ble_gap_conn_param_update(gs_central.conn_handle,NULL);
...
 
 "If NULL is provided on a peripheral role, the parameters in the PPCP characteristic of the GAP service will be used instead."
Next I'm waiting for BLE_GAP_EVT_CONN_PARAM_UPDATE event from central to find out what parameters were chosen. Here I have not experienced any changes of parameters. But establish software timer. After 20s (could be adjusted of cource) I've send 
 uint32_t res=sd_ble_gap_conn_param_update(gs_central.conn_handle,&alt_c_connection_param);
 
 to central with slightly different connection intervals (yet not tested what if use the same as at connection). And it responds with connection interval in range that I asked.
Now power consumption decreased in one order of magnitude.
I have tested this on Windows 8, Android 4.4.2, 5.1, Mac and it seem to work.