for additional deliveries which are intended either as a partial replacement of supplies or installations or as the extension of existing supplies or installations, where a change of supplier would oblige the contracting authority to acquire supplies having different technical characteristics which would result in incompatibility or disproportionate technical difficulties in operation and maintenance; when Union institutions award contracts on their own account, the duration of such contracts shall not exceed three years;
i gcás soláthairtí breise atá ceaptha mar ionadú i bpáirt ar sholáthairtí nó ar shuiteálacha nó mar shíneadh ar sholáthairtí nó ar shuiteálacha cheana, dá gcuirfí athrú ar sholáthraí de cheangal ar an údarás conarthach soláthairtí a shealbhú ag a bhfuil saintréithe teicniúla difriúla agus, dá bhrí sin, go mbeadh neamhréiteacht nó deacrachtaí teicniúla díréireacha in oibriúchán agus cothabháil; nuair a dhámhanninstitiúidí de chuid an Aontais conarthaí ar a gcuntas féin, ní mhairfaidh na conarthaí níos mó ná 3 bliana;